stake asks for proof of income for customer verification as i see from their verification page. are you people seriously providing it to a random casino?
It's for KYC/Anti money laundering reason, it's just normal. If you are brand new account but you just deposited the money which they think it's likely from hacking or other illegal things, you will be asked for that documents. It's not for every deposit, just in few extra cases.
It's not only on casino but also on exchange it self.
Any correlation between a gambling and an exchange site?