I’ve thought that too. I’d say they are trying to balance things out. Remember they take a %age on each trade, so for you to buy those coins they took a fee. So I guess they see it on a balance of earnings.
If you were to deposit safex then withdraw safex without doing trading then I’d say after doing that a few times you might find your account locked under the disguise of money laundering. Since that is what it would look like they have to investigate due to the regulations they operate under. But also because you are simply costing them money and if you do it too often they get pissed off.