SteadyMobbin said it well.
I use FL Studio and the reason I use it is because I'm VERY comfortable with using it. The workflow just works for me. I've tried other programs and even some hardware like MPC, but I never felt comfortable. I can easily do what I hear in my head with FL or just make some on the fly shit.
With that said, that just motivates me even more to try to make some quality shit in FL because everyone thinks FL is garbage.
It mostly comes down to how you mix your shit, to get a respectable sonic quality sound. A lot of those videos on YouTube n shit of FL users, their lacking in that regard. That's where it gets it's bad publicity because it's so easy to download and use, therefore there's going to be A LOT of horrible shit being made with it, the more users there are. A lot of those people truely think FL is the one stop solution to making beats and they think that whatever it comes with (built-in samples, instruments, FX,...) that's all there is to it. Just very naive.
If Reason, Logic, Cubase, Pro-Tools,etc... where more easily accessible via download, you'd see alot more bullshit being made with those programs as well. FL is only a 100mb download and simple registration to crack.