Gambling site is not a bank, nor it is an exchange. Most gamblers, more than 90% of them, deposit on a gambling platform only what they can afford to lose. They are not like "The more money I invest in it, the more profit I will get." Only sick people think that way, only so called "problem gamblers" see gambling as some sort of a business, and, fortunately, there's less than 10% of them among gamblers. So, can it be mandatory for gambling sites to show proof of money to those people, to problem gamblers? I don't think so. Those people need professional medical treatment rather than "proof of money", something that will likely only worsen their condition.