That's what I was thinking of actually. Is it against the law for them to offer such a thing? I doubt it?
They will not do that because they can now simply freeze any transaction on the grounds that it is "high risk" and here the depositing party must do everything to prove that their money is clean "origin of funds, more data, IP addresses, etc."
AFAIK, legally, they MUST block any suspicious transaction and then ask you for more details (transactions history, proof of wealth, etc.) otherwise they would potentially face something like this[1].
True, but AML's initial verification process will reduce their control over deposits; these platforms are not trying to comply with regulatory restrictions as much as they want more control.