Because they are widely available, and have a good reputation among the "non audiophile" crowd. Sure we hate kicker here, and thats all fine and dandy, but they arent bad speakers. Can you get better? absolutely. Can you get better FOR THE PRICE? absolutely. Does your average guy Jamal care about that? nope. Does Jose have time or desire to browse online and do any research? nope. His friends gf Rebecca has a set of comps and they bang yo. Kicker is available at his local best buy, and thats great with him.
As for popular in OKC? Rockford, JL, Kicker, Pioneer.. big box store stuff. A good bit of dd as well, because they are local.
In Berlin? JL, RF, GZ, etc.