Hufflepuffs are quite resourceful and reliable, very good qualities to have for a teacher trying to teach a difficult subject.
Slytherines are quite tricky and manipulative, and knowing how to use that to slip knowledge into a student's mind would be quite like them.
Gryffindors are courageous, and what sort of courage it must take to teach a classroom full of spell-potent young wizards.
In short: There are more qualities to being a teacher than just "knowing everything".
And, more to the point, the most scholarly student of them all in the series, Hermione Granger, was in house Gryffindor.
So clearly there's more to being chosen for Ravenclaw than simply 'You are the smartest'.
scifi.stackexchange.com/users/20533/Zibbobz
Intelligence isn't limited to those who are in Ravenclaw, and it isn't the only characteristic that the Sorting Hat looks for when assigning students to Houses.
It's perfectly possible to be incredibly intelligent - more than enough to potentially be Sorted into Ravenclaw - but demonstrate something else that ultimately means you would be better suited in another of the four Houses.
Just look at Hermione, who was the smartest student in her year at Hogwarts, but was Sorted into Gryffindor because she demonstrated potential for great bravery, which evidently outweighed her intelligence.
scifi.stackexchange.com/users/5833/Anthony Grist
According to Pottermore, Professor McGonagle was the premier Transfiguration academician of her time (and before her, we of course have Albus Dumbledore's academic achievements).
Both were in Gryffindore, and both - leaving aside all OTHER considerations - were clearly more academically qualified to teach Transfiguration than any competitor, from Ravenclaw or otherwise.
scifi.stackexchange.com/users/976/DVK-on-Ahch-To
There are two or three assumptions here that need to be debunked.
Firstly, the idea that teachers have to be the smartest - in fact, if the wizarding world is anything like the real world, many of the smartest and brightest may well have shunned teaching for other pursuits.
Secondly, the idea that intelligence is inherently a bookish thing, and that it is the most important trait of a teacher (really it's just one of a number that teachers need).
And thirdly, the idea that the Houses and their students are all so obviously not alike.
The beauty of the different House traits is that they are all so broad as to mean that any one individual could show characteristics of all 4 of them.
ç
Yet he was also "the bravest wizard I have ever known" (according to Harry) due to his working as a spy against Voldemort (Gryffindor's primary trait).
His brilliance at school in potions (as demonstrated by the Half-blood prince book he left) show he had the ingenuity characteristic of a Ravenclaw.
And his loyalty to Dumbledore and to his affections for Lily, a loyalty and dedication that lasted right to the end, show he had a bit of Hufflepuff in him too.
And let's not forget the very real possibility that people change, with time.
Snape again, may be a good example of this.
What House would he have been sorted in, if he was Sorted around the time of the 7th book, instead of as a child?
scifi.stackexchange.com/users/13951/The Giant of Lannister
This question begins with an incorrect assumption " Presumably, anyone who ended up as a Professor must have been pretty smart .
" This is easily dismissed by reviewing Professor of Divination, Sybill Trelawney , She clearly does not fit in the category " pretty smart ".
Another large character/professor may also be identified, as a tough fit for " pretty smart ", who I will leave unnamed for those who have not progressed through the entire series.
As " pretty smart " is not a requirement for professorship, a house has little to do with becoming a professor.
Not to mention the facts presented in other answers concerning the distribution of Intelligence across houses.
scifi.stackexchange.com/users/13442/James Jenkins
Ravenclaw is for all the smart wizards. Presumably, anyone who ended up as a Professor must have been pretty smart. So why are there Professors not from Ravenclaw?
Why aren't all Professors Ravenclaws?
scifi.stackexchange.com
<harry-potter><sorting-hat>
scifi.stackexchange.com/questions/49653
scifi.stackexchange.com/users/16518/ike
A person might be incredibly intelligent but demonstrate something else that ultimately means they would be better suited in another of the four Houses.  The different House traits are all so broad that any individual could show characteristics of all 4 of them. For example, Hermione was the smartest student in her year at Hogwarts, but was sorted into Gryffindor because of her potential for  bravery. The Hogwarts houses were allotted based on values and being a Ravenclaw doesn’t automatically mean you are intelligent since intelligence exists in various forms depending on values.
The Hogwarts houses were allotted based on values. Intelligence isn’t limited to those solely in Ravenclaw. Being a Ravenclaw doesn’t automatically mean you are intelligent since intelligence exists in various forms depending on values.