Sometimes, trading on different exchanges helps you to spread the risk, rather than just putting all your trading money into one single account.

All exchanges cannot be hacked or have problem at the same time, and the fact remains that you do not have any control over your funds since exchanges are centralized, so in that case, so as not to lose all your trading funds, should incase an unfortunate incident happens to such exchange, makes it quite important to at least trade on 2 to three different exchanges.

For me, I would say, Bittrex, Binance and Kucoin have been doing it for me, and I feel Kucoin is one exchange that is really growing in volume at the moment which the OP did not also mention.