Some casinos allows you to withdraw when you have win with the bonus and meet up the required wagering amount while some will still ask you to wage again or asked you to deposit first before you can withdraw and as was said, casinos have different ToS.
Do you mean that they include it in their terms and conditions that after a player meets to wagering requirements for bonuses or deposits, they will still ask for extra wagering or mandate the player to still make extra deposits?
If yes the casino makes such rules statement their terms and conditions then it will be left for gamblers to either continue to use such a platform or move on to the next one, this is because, with such a rule in place, it is almost impossible for the gambler to ever make anything out of the casino or even to succeed to withdraw their deposits or winnings too, I have not come across such a casino with terrible term and condition as regards to withdrawal, but if I do, I will never play on such a casino even though they offer me 200% bonuses.