Well, there are hundreds of exchanges and many more coming up, but not all exchanges are good. Only a few exchanges have got good reputation and the majority of investors have been trading there like Binance and Bittrex.
Not all exchanges will even be able to stand a chance for the real world when mainstream adoption kicks in and just very few will be able to withstand that pressure as the same way we are seeing shit coins today is practically the same way we are also seeing some shit exchanges.
Moreover, having quite a huge number of exchange platforms is not a problem at all, as long as we keep having very good ones with great features popping up, the more the competition will keep growing and that is good for the space. Also, investors are also growing by the day; otherwise exchanges will not even be a thing.