Well there was a signature campaign I participated and it was only for a week, when I joined the payment was sent directly to their gambling site and there are requirements which one must meet to enable them make withdrawal, this condition aren't stated on their signature thread but after payment and I wanted to withdraw I noticed that I must reached a certain threshold for me to be able to have my funds withdrawn.
And of course, it's like a compulsive gambling where the said user has to gamble to meet their requirements to be able to make withdrawal so I had to gamble with such amount sent to gamble site, I was actually lucky enough to had winning and meet up their requirements to be able to withdraw my funds. Most times signature campaign payment sent to their gambling site are indirectly want to gamble and want to take back their payment back to them because they knew that gamblers must lose while gambling.
I can withdraw current sign payments freely (no withdrawal fee either), but earlier I had won this BTC price prediction contest from same casino — I received amount, tried instant withdraw (knowing gambling it would likely cause me to lose it), wasn't able to as amount was below the minimum threshold, so I made some bets and thankfully I was also lucky enough to win those and was able to withdraw.
...maybe the next question is can we blame them for putting it into the casino account? No, still up to the gambler to what to do to their payment.
I would not blame them, and if I was at casino's place, I would want payments sent directly to casino too as it makes user open casino and might make few bets as well. Just don't put restrictions as in wager and shit, and it's all good.