> You have to take their words for it but how can you trust crooks?

Because these are repeat actors. If they take a ransom and then re-sell it, no company will pay them ever again.

Don't think of experienced criminal enterprises as "groups of irrational scoundrels." They are companies, with employees, who understand game theory.

At some point, these people will come up with a ransom-as-a-service that you can subscribe to make monthly payments. It's no different than having to pay criminals monthly for security to prevent them from harming your themselves.