Earlier quoted context omitted.
Credit cards act as a "cost" of sorts. Credit cards are a limited resource, it is not free to acquire more credit cards. By requiring a valid credit card you are basically relying upon the verification that credit card issuers do to prevent unlimited abuse.
Its not free to acquire credit cards? In what country? I constantly get free offers on the mails, plus there are services to generate temporary card numbers for throwaway
It's the automated bots that a CC prevents. Even with "free" credit cards or generated numbers, there's a lot of friction in going through that to abuse the service's trial period.