if legit companies were required to prove that their contractors followed ALL laws (with epic fines for violations) then these boiler room companies would go "POOF".
How would they prove that? You can only prove when they DON'T. And most of the time, you can't prove they are breaking the law because you can't identify who it is that is breaking the law. Either the predictive dialer dumps the call after you've answered and you have no information about the call (other than the faked called ID), or you get a recorded message with no information about the caller, or you "press 3" to talk to someone who refuses to identify who they actually work for.
For those who think it's huge amounts of fun to waste the time of the scammer by talking to him, just remember that when he finally disconnects he's pressing the "contact failed" button that puts your number back into the system for another call and you get to talk to him again. He gets paid, you don't, you lose.
Yes, there are a few morons who use such tactics as part of their real marketing operations, but by doing so they leave the realm of "legit". The number of truly legit operations is already very small, so making every one of the legit ones go "poof" will do nothing to solve the problem. And that ignores the issue of the loopholes that still allow robocalling for some users.
It's kinda like putting more gun control laws in place. The law abiding gun owners are already obeying the law and the criminals just ignore them. "One more law" isn't a solution there, and it won't be a solution to robocalling.