It seems likely their policies are a response to the risk that abusers will mine cryptocurrency, then skip out without paying the bill. Register multiple accounts, repeat ad nauseum.

Even requiring a credit card isn't too helpful because cryptocurrency can be cashed out right away, while credit cards transactions can be reversed.

Also, for new accounts which have not been billed yet there is a lot of uncertainty about whether the account was really registered by the cardholder.

This is a nontrivial fraud problem, and the cloud provider response is a first approximation to a solution. I would expect that as they engineer better fraud signals and risk scoring, they'll eventually be able to offer gpus to new accounts.