If the AR owners here are going to be honest, and I'm one of them, they'll tell you that part of it fills that little kid GI Joe fantasy we all had. They look cool and they are fun to shoot. They serve no other purpose.
All you have to do is read the AR forums and you'll see the guys who deck out their AR15s with all kinds of junk to make them look 'tactical'. Laser sights, red dots, flashlights, mock grenade launchers, tactical slings, bayonets, double magazines. You name it, the SHTF guys are prepared.
If you are a serious shooter, you'd not do that, but get 20 inch custom barrel as the target shooters do. But most of us have 16 inch barrels with collapsible stocks.
This speaks to the real reason
I haven't succumbed to that disease
Mine is pretty bare bones the way I like it.