The point is that, if there is a per-call cost that everybody has to pay, it becomes much harder for spammers to justify automatically calling hundreds of thous

The point is that, if there is a per-call cost that everybody has to pay, it becomes much harder for spammers to justify automatically calling hundreds of thousands of numbers per day, while regular people who make one or two calls a day won't notice. "enforcing the laws we have" isn't enough because spoofing exists and many of the spammers operate across borders.