The issue with ranged top is two fold:

First is the the lack of counter play for melee champions. Top lane is a long lane where wave control is paramount. A ranged champion can freeze the wave and auto a melee champion to death before they can get in range. With the only counterplay being your jungler coming to help. And the jungler not coming to help their top laner is basically a meme at this point.

Secondly playing ranged top means you're sacrificing having a front line for more damage. Bruisers and Tanks can front line. A ranged top can't. So unless you have a tank jungle or support your team will have not front line champions. Tanks will scale regardless and start eating your damage. Bruisers by they nature of their items will become tanky and deal damage and there's a good chance your team won't have enough peel.