mostly what happens is they stay in the exchange to avoid the large transaction fees.
The problem is they will get something out of your trade and then they will take another from your withdrawal.
Miners fee + others. Can't they just change it into dynamic mode? One of the questions I have been trying to look for answers.
Another is like HitBtc which is a robbery. Deposit fees. Ergh. That is just too much if you add the payment that you will have to do from all that little move you made.

Even if we are listing exchanges, HitBTC should not even be counted among. This is an exchange that is engaged in day light robbery like you said, no support, not even a good platform to trade on, several attempt to keep stealing users fund and so much more and I still wonder why people still make use of this exchange by the way.
Normally, we should expect that exchanges will always tend to make a whole lot for themselves, and even though we may want to see something dynamic, they are in it for the business of rendering service and bills got to be paid, isn't it ? However, being lenient with the fees is one thing that we should clamor on, and for what it is worth, we have seen exchanges like Binance doing a great job so far.