"Can o' Worms"
No doubt that it's been in use for a very long time (early 60's till now). A lot of service guys are familar with it.
It's easy to assemble (put one together). Easy access to ammunition, or to reload for.
Inter-changeable parts and the list goes on and on.
Yes, I like the AK (and I have quite a few) but with the AR, I don't have to worry about if it's made in Poland, Hungary, Romainia or where ever.
And, there is the always SHTF deal, parts will be available if you know what I mean.
Just a few of my opinions, and I'm sure that others will have theirs.