or why they're so desireable.
In my case it's mostly that I grew up shooting DCM with an AR-15. A bit of nostalgia, a bit of familiarity, and that's about it.
Should I ever find myself in the unenviable position of needing a gun to defend myself I'd much rather have a 12ga or a .45 pistol, and I can't think of anything I'd consider hunting with a .223. For deer my weapon of choice is an old M1 Garand that's been around longer than I have and for game birds it's back to the shotgun. There's really nothing else worth hunting here unless you like rabbit (I don't) and I'd opt for a high power pellet gun or a .22 for them if I were going to hunt them. If I were to find myself in need of an actual battlefield-worthy gun I'd want an AK-47 or, if we were going short range, an AA12.
Literally the only place my first choice of guns would be an AR-15 is on a shooting range, and then only if I'm shooting for fun. It's just not a practical gun for much of anything else. Even so if I ever got the chance to get one I'd take it.