BCH is rocketing now, and as you can see from other altcoins they're going massively down because people are selling theirs off in order to jump aboard BCH. This will put massive stress on any exchange.
Simply put there is not enough processing power available on these services, because during your average day it wouldn't make sense to have too much of it available and lose money on it. This means that once the need does spike like this, adding more is a bit too late already.