You could say it is built into the smithing skill. When you make the hide helmet for Adrianne in Whiterun during the smithing tutorial, she tells you to improve the fit and you then craft it into a Fine Hide Helmet. Only wearing armor you've made or upgraded, as sthompson suggested, is probably the best way to roleplay this.

Ok but why?

Little bear people living on a moon of a planet that doesn't exist! That does not make sense! Why are we talking about Ewoks in a Skyrim forum? That does not make sense! Now we can debate between sci-fi fantasy Captain Kirk Dumbledor all YOU want to, but if your male armor has magic accommodations for female booby parts you must acquit!

The defense rests.

More over why does armor you looted off a mail magically turn female for female characters and NPCs?

Because the technical aspects of setting up different sized armors and gender specific restriction is just stupid when you can make one armor morph to your character.

You said it yourself. Its just a game. Get over it.

Well I've seen people debate over the rivers in the game and how they flow. So this isn't exactly out of the realm of discussion

I want that water update from jam week to be implemented.

Why can you jog indefinetly? How can you survive without eating or drinking? How can Dragons fly given the irregular shape of their wings? Why do the vast majority of Skyrim's citizens sound the same? How does a brain fit in an Elves oddly shaped skull? And for that matter, why are there Mammoths with four tusks instead of two? Why is the wildlife so agressive?

Its a game.

It's one of the gameplay over realism things lowering tedious gameplay.

Personally I roleplay and take new armors to a smith for refitting before I put them on. You can still do these things if you want to.

don't forget there are no toilets in skyrim either,or on endor for that matter

1. This is actually explained. They use magic to fly, for the very reason you questioned. Their wings are unable to support actual flight, so they use magic.

2. It would stand to reason that an elf would not have the same shape brain as a human.

I know just the right thing for you! Here, try this Scaled Helmet on! Too much corrundum in it? Or not enough? Maybe we could make it fit better and be more comfortable by stuffing the inside with thick layers of ice wolf fur. There's also several pair of nifty gauntlets right here, coming in black, semi-black, half-grey and grey variants. Give me that hand of yours, it'll be a quick measurement and we're done. How about a custom made crest on that cuirass? The Dragonborn deserves no less, after all. If I had a sister, I'd sell her in a second. And she would be custom fitted to you as well!

Well i guess it would have been annoying for many people to search for the right size of the armor especially if you get a rare enchanted and later realize you couldn't use it, quite frustrating actually.