Hey Steve
For reasons between you and I only to understand, I GET EXACTLY WHAT YOU ARE TRYING TO FIGURE OUT 
So let me explain as this exact thing just happened to me, and I will include why this policy does INDEED hurt the casino more then help.
I was playing at a casino on a $10 new year bonus they awarded me.
The maximum cashout was $100 and the wagering requirements were standard of most casinos online.
With a strike of luck I met the playthrough requirements as the countdown hit $0 and since I had hit an earlier jackpot of $900 I was well over the maximum of $100. So obviously now there is no reason for me to keep playing since winning more would be painful knowing I would not get it.
So I submitted a withdrawal. FOr $100. Now here is where Steve’s question comes in.
So now what do I do. I have a pending withdrawal. I can’t deposit. And I can’t play any more.
I either can leave the casino and go play somewhere else….or leave the casino and sign off. Because now I am required to wait for the process of the casino to get my withdrawal and send it to my bank or whatever method I chose and as we all know sometimes that can take 3-4 days.
Many times I Have asked the casino support to just leave the $100 in my account, clear out the extra funds, and let me continue playing from then on being the $100 is cash of my own and I am free to lose or win with no retstrictions, and everytime they all say that I have to wait for the process. So then I wait. And you know what happens, I get that money in my online bank and maybe deposit some of it at that casino but almost everytime i have done this I have deposited more then 50% of it somewhere else.
The casino I originally cashed out with had they of done the above suggestions, we all know 9 out of 10 times would of gotten everything back including the bonus monies if not a dpeoist or two on top of that with the way the odds work.