The two biggest drivers for me - they're chambered (primarily) for a high velocity 22cal centerfire round suitable for coyotes, and they're semiautomatic, which has a benefit for coyote hunting - and I'm a coyote hunter first and foremost. I was calling coyotes for over a decade before any dumb gun magazine decided to call it "predator hunting" and drag every bozo with a rifle out of the woodwork to educate coyotes, and for laying fur in the dirt, the AR is very hard to beat. (For deer hunting, I don't often use AR's, but I only do because I'm so used to them from calling coyotes - the fact that it's a semiauto then becomes completely moot).

For the price, there isn't a more reliable, more affordable, more accurate, or more versatile semiautomatic rifle on the market.

Starting life as a military platform made them available and gave them a toe in the door, the fact that they earn all the respect they get gave them staying power.

The fact that AR-15's facilitate optics easily is another huge advantage. You have to admit, putting a scope on a Garand, M1A, SKS, AK47, etc etc is less than elegant.

The proprietary nature of "branded" semiauto designs makes them, by default, less permeating - EVERYONE can make an AR and sell their version, but if you want a semiauto rifle, you can't buy an R1 from Winchester, you can't buy an SXAR from Remington, and you can't buy a 750 from Benelli... Ruger makes Ruger, Benelli makes Benelli, rem rem, winchester win... But EVERYBODY can make AR's, so I can buy the flavor of AR that I want, then pretend it's in some way better than the other flavor.

So... If there was a model that could do everything that I ask of my AR's, do it better, cheaper, or more reliably, then I'd be less of an AR fan. I haven't found that particular model yet.