Most crypto businesses charge a hefty withdrawal fee, which is not much related to the actual tx fee. It happens usually at exchanges, but it's not limited to them.
The withdrawal fee (in Bitcoin) is not related to the amount you withdraw. It would have been the same (in Bitcoin) even if you would have been withdrawing 10 BTC.

You should have been reading the rules before using their services, you should have been reading the rules before attempting withdraw of such a small amount.
While I agree the fees should be easier to find even if one doesn't have account there, they are present on the thread about crypto casino fees.