Ranged tops tend to function far better as such than they do as proper ranged (mid or bot). They're top because they satisfy the niche. They're good against picks like Darius and Garen who tend to pick better fights when it stays closer to them. Meanwhile, a ranged top like Quinn has a bit more room to act against them and a few more resources to use against them. Contrarily, they'd probably just feel under-ranged and out-poked anywhere else, as well as probably not having either the CC or the burst to hack it in either role (where they're likely relied upon for one or the other).
I think they have a niche. Besides, isn't Yasuo popular? Wouldn't he have an easy time with ranged tops since he can wind wall them? Others like Blitz and Naut can force the fight, too, which will put ranged at a disadvantage since they tend to rely on fairly protracted moves (again calling to mind Quinn).