Somebody told me it is because they are on Omni protocol which taking a BTC fee to send fast transactions. I don't want fast transaction as I'm not in the rush so I should be able to reduce the fees.
I like Bittrex too but I lost a bit of confidence to them with this issue.
So far, Ripple, XEM, Bitshares and SAFEX are really expensive to withdraw
No answer from the support after one week