It doesn't matter if there are lot of exchange in cryptocurrency, for what matters is that you earn in the exchange. But as much as possible it is good to trade coins at the exchange on which are always on top 20 at least, due to it is really an advantage if the coins is listed in that platform, I assured you on that.
it doesnt matter ? of course it does matter because if there were too many exchanges we can also expect that most of these are only scam or have a bad service , so instead of wasting our time trying those , why cant we just have a few exchanges that is legit and already trusted . in that way veteran and newbie traders are safe everytime they trade thier coins .
some coins especially those coins that you can only get on an airdrops and on a bounties are usually listed on the unrated exchange or on the exchange that are not on the top list .