lol here we go.
Allow me to quote Linus Torvalds: the great is the enemy of the good.
It's like mp3. Not the most optimal, but by far the best supported. And so is avi. You give someone an avi, they know what to do with it, they can play it probably. You give someone matroska and they have no idea. The point is to be
useful far and above being
perfect.
Btw you can set mkv or ogm or mp4 or whatever the heck you want instead

But the default is gonna be the most useful pick.