I always found my popcorn a bit soggy and noticed the microwaved packets aren't. So yesterday I made a little experiment with a friend of mine.   I took popcorn kernels and microwave popcorn sets then conduct these experiments :    Microwaved popcorn (900W, 2'20'') Air popper machine (the cheap one you find on all Chinese store) Stovetop without oil Stovetop with oil  Stovetop with butter Stovetop with microwave popcorn (at this step I discovered that this kind of popcorn is completely coated with palm oil) Air Popper machine with microwave popcorn   Here the results :    Crisp perfect Very soggy and quite small Burned, they didn't really popped  A bit soggy same as 4 but with a better taste Very soggy  Almost same as 6.    Eventually I still don't understand why I can't make popcorn as good as the one I can eat in theaters.   Any idea? 
Not truly and answer, but I am trying for an explanation of what likely you are seeing:  Popcorn pops because there is a small amount of water it those try kernels that when heated goes from liquid to gas and because it is contained it does so explosively.  Key is getting the proper amount of heat to go boom.  Too much, burned.  Too fast, incomplete boom.  Too little, no boom.  Poor corn, be it too dry or too wet, no boom or incomplete.  Now, sogginess?  Well, the boom releases that water as steam.  If it gets trapped, soggy popcorn.  Also, many applications as you noted use oil.  Too much and soggy popcorn.  Why oil?  Because it helps distribute the heat more efficiently and uniformly for a better boom.  Some think it also helps trap the water for a more complete explosion, I will just say maybe, but not the prime reason if so.  It also flavors and helps any seasoning stick.  Air popper:  I have never had soggy from it though those cheap models are notorious for uneven heating, kicking out unpopped kernels, overloading and burning, etc.  I could see the soggy issue though if it is not properly exhausting the vapor especially if overloaded, but I find it odd because their claim to "fame" is specifically dry popping os that one if a bit odd.  Dry stove-top, that is usually going to burn due to uneven heat.  I have heard of people being able to pop on a stove with little to no oil, but I have never seen it.  Normally need oil to have a chance on the stove to get even heat.  Microwave:  The pre-packaged stuff has a ton of oil. In addition, the microwave works by vibrating the water molecules, to popping corn in a way is almost what it was designed for.  Know, you can also pop corn without the oil quite nicely especially with gadgets to help focus the microwaves well, but the pre-packaged bags are convenient and the companies make more selling those than the gadgets.  ;)  Note though the bag is vented.  It is actually a key thing.  Also, you typically will open the bad fairly quickly when done, which lets out the steam. If you fail to do this while still fairly hot you may find the microwave corn can get soggy too.  Key things for stovetop tends to be even heat and venting.  Theaters use a larger version of a popper on which the device @moscafj mentioned is designed.  Those designs stir the corn which increases the uniformity of the heating, so less chance of scorching, fewer inclomplete pops, but also they have hinged lids.  This lets steam escape and is important to your experiment.  Tight fitting lids on the stove equal trapped vapor which condenses and dumps water back onto the corn, instant soggy.  On popping in butter, there you are dealing with a lower smoke point so getting the right temp for popping without scorching the oil may be tough, and the butter itself will release some of its water so may produce some good tasting, but soggy mess. 