user26865: After the initial moves of the French Defense: Exchange Variation, my opponent played 4.Bb4+. I followed with 5.Bd2, but after analyzing it, I saw that it is not in the master games opening on chess.com and 5.c3 and 5.Nc3 are considered better moves.
[fen ""]
1. e4 e6 2. Nf3 d5 3. exd5 exd5 4. d4 Bb4+ 5. Bd2

It looks like the most natural move to me, because:

It forces the bishop away or to take my bishop which I can recapture with my knight, therefore developing it if he decides to take
c3 looks like a less natural move because although it pushes back the bishop, it prevents my knight from developing on c3 in the future
Nc3 looks like a less natural move because it pins the knight to the king, and if he takes my knight, he gets my pawns double stacked on the c file, which I always have thought you should try to prevent

So, why the move is weaker?

user26801: I would say that 5.Nc3 is better than 5.Bd2 because 5.Bd2 would allow Black to exchange Bishops very early in the game. It is a general principle that more piece exchanges lead to less complicated middlegames and to more chances of draw, which is naturally something that favors Black. The move 5.c3 does not look optimal to me since, as you said, it blocks the development of the Knight. So, I really don't know why the engine favors it.
By playing 5.Nc3 you develop your Knight to one of its most natural squares, but you allow the pin. This will either force Black to capture your Knight (thus, exchanging a Bishop for a Knight which is generally better for White) or ignore your Knight and further develop. However, White can later respond with a3 followed by c4 and expand his/her grasp on the Queenside. This will probably lead to short castling for both sides, but White should be still slightly better.

user2569: Depending on what database you look at, all three moves (5.c3, 5.Nc3, 5.Bd2) are playing in this position. Nc3 and c3 are the most common, but Bd2 is played sometimes.
A lot of the play in the French Exchange is centered around the central squares and the open e-file. Quite often, White will play c4 and Nc3 and try to deploy their bishops at d3 and f5 or g4.
The problem with playing 5.Bd2 in my opinion is that the bishop is much stronger on a square affecting the center rather than trying to counter Black's bishop. Additionally, if Black plays 5...Bxd2, White can recapture with the Knight, which would put the knight slightly out of position (as it's better on c3 than d2), or the Queen, which would put it slightly out of postion (it's not really affecting anything on d2). If Black does not capture and plays like 5...Bd6 (it's best square), then White needs to reposition the bishop, which is doing nothing on d2.
Playing 5.c3 is fine. It moves Black's bishop, has central solidity, but creates a gameplan where white will need to do more maneuvering to get its pieces (i.e. the b1 Knight) into good positions. Ultimately, the Exchange French tends towards a draw and passive play, and, while 5.c3 seems active, it creates a passive setup for White.
I think @cyclops is right in the value of 5.Nc3. It keeps up the pressure on the center and develops a key piece to its most influential square. Yes, Black can take it and double White's pawns, but a) Black's dark-squared bishop is a really valuable piece in this opening, b) it still allows white to play c4 comfortably to hit the center. It may look messy, but it's better overall.
The French Exchange is usually fairly slow and equal. Bd2 may put White a little out of position, but it does depend on what kind of game White wants to play, i.e. if White wants to be active, passive but solid, or simply counteract anything Black does.

user12629: It appears to be 4...Bb4+ that's the unusual move here. The chess.com database only shows one game with it, and that's the game that continued with 5.c3. When you have the position after Bb4+ on the board and it shows 5.Nc3 with a bunch of games, it's actually showing games that transposed into that position - the Nc3 was played earlier in the game.
Given that there's only one actual game in the database with Bb4+, there very well may be nothing wrong with Bd2. It hasn't been played simply because the position almost never came up.

26865: <p>After the initial moves of the French Defense: Exchange Variation, my opponent played 4.Bb4+. I followed with 5.Bd2, but after analyzing it, I saw that it is not in the master games opening on chess.com and 5.c3 and 5.Nc3 are considered better moves.</p>
<pre><code>[fen &quot;&quot;]
1. e4 e6 2. Nf3 d5 3. exd5 exd5 4. d4 Bb4+ 5. Bd2
</code></pre>
<p>It looks like the most natural move to me, because:</p>
<ul>
<li>It forces the bishop away or to take my bishop which I can recapture with my knight, therefore developing it if he decides to take</li>
<li>c3 looks like a less natural move because although it pushes back the bishop, it prevents my knight from developing on c3 in the future</li>
<li>Nc3 looks like a less natural move because it pins the knight to the king, and if he takes my knight, he gets my pawns double stacked on the c file, which I always have thought you should try to prevent</li>
</ul>
<p>So, why the move is weaker?</p>
 26801: <p>I would say that 5.Nc3 is better than 5.Bd2 because 5.Bd2 would allow Black to exchange Bishops very early in the game. It is a general principle that more piece exchanges lead to less complicated middlegames and to more chances of draw, which is naturally something that favors Black. The move 5.c3 does not look optimal to me since, as you said, it blocks the development of the Knight. So, I really don't know why the engine favors it.</p>
<p>By playing 5.Nc3 you develop your Knight to one of its most natural squares, but you allow the pin. This will either force Black to capture your Knight (thus, exchanging a Bishop for a Knight which is generally better for White) or ignore your Knight and further develop. However, White can later respond with a3 followed by c4 and expand his/her grasp on the Queenside. This will probably lead to short castling for both sides, but White should be still slightly better.</p>
 2569: <p>Depending on what database you look at, all three moves (5.c3, 5.Nc3, 5.Bd2) are playing in this position. Nc3 and c3 are the most common, but Bd2 is played sometimes.</p>
<p>A lot of the play in the French Exchange is centered around the central squares and the open e-file. Quite often, White will play c4 and Nc3 and try to deploy their bishops at d3 and f5 or g4.</p>
<p>The problem with playing 5.Bd2 in my opinion is that the bishop is much stronger on a square affecting the center rather than trying to counter Black's bishop. Additionally, if Black plays 5...Bxd2, White can recapture with the Knight, which would put the knight slightly out of position (as it's better on c3 than d2), or the Queen, which would put it slightly out of postion (it's not really affecting anything on d2). If Black does not capture and plays like 5...Bd6 (it's best square), then White needs to reposition the bishop, which is doing nothing on d2.</p>
<p>Playing 5.c3 is fine. It moves Black's bishop, has central solidity, but creates a gameplan where white will need to do more maneuvering to get its pieces (i.e. the b1 Knight) into good positions. Ultimately, the Exchange French tends towards a draw and passive play, and, while 5.c3 seems active, it creates a passive setup for White.</p>
<p>I think @cyclops is right in the value of 5.Nc3. It keeps up the pressure on the center and develops a key piece to its most influential square. Yes, Black can take it and double White's pawns, but a) Black's dark-squared bishop is a really valuable piece in this opening, b) it still allows white to play c4 comfortably to hit the center. It may look messy, but it's better overall.</p>
<p>The French Exchange is usually fairly slow and equal. Bd2 may put White a little out of position, but it does depend on what kind of game White wants to play, i.e. if White wants to be active, passive but solid, or simply counteract anything Black does.</p>
 12629: <p>It appears to be 4...Bb4+ that's the unusual move here. The chess.com database only shows one game with it, and that's the game that continued with 5.c3. When you have the position after Bb4+ on the board and it shows 5.Nc3 with a bunch of games, it's actually showing games that <em>transposed</em> into that position - the Nc3 was played earlier in the game.</p>
<p>Given that there's only one actual game in the database with Bb4+, there very well may be nothing wrong with Bd2. It hasn't been played simply because the position almost never came up.</p>
