Another issue with YouTube is that media, especially video is vastly more resource demanding than anything mostly text based.
With something like Twitter or Reddit (as long as you don’t directly host all media) the quality and importance of each post relative to it’s resources needed don’t really matter that much.
Especially with high bitrate video footage on the other hand it does matter. So having a drive for profit somewhere in the chain does in someway help shape the system to be viable financially.