What if the government makes casinos act as withholding tax agents? Winning gamblers wouldn’t be able to evade their tax liability. This could likely happen if the government notices a gap between tax collection and their expectations. They’d have the data from gambling sites, which are required to report it, so they’d know exactly where to step in.
That could happen reminds that regulator/government can ask that to the casino because casino can check to all of their members. So when the gamblers win much money, they must pay the tax to casino and the casino will report and gives the tax to the government. The gamblers can only obey the rules from the casino so they don't have to pay the tax to the government because their winning deducted to pay the tax. Everything can be possible as the government have the power to control the casino under them.