It wouldn't, with the exception of Retro because Retro hosts can choose a theme that actually restricts songs that don't fit. But even in that case, people start getting persnickety if they think a theme is too limiting or that there have been too many restrictive rounds recently because they can't enter the songs they want to enter. The only way to get more diverse entries is to have more diverse winners. But even then, that would only go so far. People aren't going to start entering songs they're not that into.