The US military doesn't use semiautomatic AR-15s with 16" heavy barrels and A2 stocks, either.
But your point is valid. The AR's popularity is due to many factors. For one, it's been around the longest of all of the .223 autoloaders, and its availability has been steady (and from many manufacturers).
Secondly, it looks like the rifle the military uses, so people buy it just for that (though I personally don't understand that rationale. Maybe having actually been in the military has worn off the mystique of the design.)
Mainly, I don't think the AR-180B is popular for two reasons. One, it hasn't been out long enough to GET popular, and two, Armalite isn't making enough of them to build a solid base of users (which translates into "popularity".
As for the AR-180B feeling "cheap". That's a subjective thing, I suppose, but then, I don't consider the aluminum and plastic AR-15 to be an especially sturdy weapon, either.
Glock certainly doesn't pass on the savings of being poly framed to the consumer. (G21s run over six hundred in my area.) I see your point, though, Telewinz.
There is a third reason, though, I think that might affect the 180Bs popularity. It's only been out for a short while, and many consumers are cautious, preferring to wait until the bugs are worked out before dropping hundreds of dollars down (an understandable viewpoint).
The AR-180 design has potential, though. It's just as modular as the AR-15, having separate upper and lower receivers. If it goes someplace in the market, you could see other makers begin producing uppers for it.