Well, nowadays majority of the crypto gambling websites offer instant withdrawals,so I doubt this is priority for crypto gambling community. There were more anonymous casinos or bookies few years ago while it is hard to find reliable gambling platform nowadays. Promotions are important to bring more customers as first step btw.
Not every cryptocurrency gambling websites that offer instant withdrawal you can explain or testify for the one you know better because not all the one you know that is cryptocurrency gambling that do instant withdrawal immediately,, unless it's new one that is looking way forward of getting new costumers. Casino gambling have varieties and it functions due to the rules and regulations of the platform to maintain their reputation