There is nothing good coming out of having too many exchanges. Most of them do not even have good volume to be enticing to do trading. And if they have volume, it is run down with bots. It is better to have lesser exchanges but have quality volume and less bots.
This is the concern I could think of right now. The volume of a certain token will be divided to these exchanges thus making it not to be unattractive to users.
Maybe that is the reason why some coins/tokens are exclusive only to a certain exchange.