HTML5 games on itch.io can only be tagged as HTML5 games, even if I have a downloadable build for it. For examplem I upload a build and mark it as a Windows build, but the game isn't tagged as an HTML5 AND Windows game, just HTML5, this way, the game gets LESS visibility, since now you only find the game under one platform tag, rather than many, like downloadable projects. So, either I get less visibility or I have no browser build on itch, and people would have to go to GameJolt to play my game's browser build. 

My suggestion? You could be able to mark a downloadable as a side downloadable build of your game, and the platforms selected on that side build would appear on the platform section and give the platform tags, giving the game more visibility. I mean, it can't be THAT hard, GAMEJOLT games can be tagged HTML5 AND operating systems (Windows, MacOS, Linux...), I bet it would take, at a maximum, two weeks.