You're incorrect, and underestimating the potential profit vs cost. 5c per outbound call, but even if the scammers get 1 or two people a day for $100 (and likely MUCH more), it's just a drop in the bucket to operating costs.
Or maybe this issue couldn’t be solved unilaterally, where one carrier could offer much better spam protection as a competitive advantage, and the industry is too decrepit for group effort that doesn’t have direct implications on their bottom line.
Do you think the scammers have a better return than $100 / 2,000 calls made?