I have been on this kind of situation before and I know how it felts like it is really annoying and you feel like you are wasting your time, money and energy, but I know this is to prevent from excessive withdrawing since there are gamblers who transfers big amount of money inside their casino and will try to win whatever they are offering either the pot money and will just withdraw immediately after winning. They are preventing this kind of scenes from happening that is why mostly you have to control how much you are going to put inside the casino just in case they will put this "lock period" strategy.
Just as casinos are being very careful about those which may try to use their casino as an improvised mixer, gamblers need to be very careful as well, since the waging requirements of this casino are high for a regular deposit, and unless someone is committed to play long term on the casino it is kind of difficult to reach them.
But how to avoid this? And the only way we can do that is by doing our due diligence by reading the reviews of other gamblers regarding the casino in which we are interested, and by reading their TOS, just in case there were some changes since the reviews were first posted online.