I recall, when I signed up for my free year of AWS, that it required a valid credit card. They claimed to only target providers that need essentially only an email address.
I think that detail makes the title incredibly misleading.
This also illustrates the rules of efficiencies. If there exists a resource one makes available for a given purpose (signing up lots of developers for free accounts) then you can assume there exists others who will figure out how to get those resources and turn them into something else of value to them.
There's no such thing as a free lunch. There's also no such thing as limiting fraud. It will always be a choice.
I think the "Amazon" spin in the title is from many other services running atop of EC2 and effectively reselling EC2 instances or access to VMs that run on EC2. They could more easily create accounts with these services and technically still run "within Amazon's cloud".
That's, after all, just an permutation of the 'use scraped email addresses to create realistic-looking fake email addresses'. I think anyone wanting to use this for damage wouldn't be stopped by some CC requirement, especially if it's not charged.