A significant portion of the American public has bought into the idea that money is the ultimate quality metric: if you're making money, you must
ipso facto be doing something right. Conversely, if you are poor, or if you are doing something that prevents someone from making money, that is bad. This is one of the reasons Donald Trump is so popular: he's richer than you, so ipso facto he must be doing something right. He must be smarter than you, because if he weren't he wouldn't be richer than you.
This mindset is evident even here on HN where, for example, "Move fast and break things" is an accepted item of conventional wisdom. Moving fast and breaking things are not good in and of themselves, they are good because if you move fast and break things you can make more money than people who move more deliberately and don't break things. (Until, that is, your airplanes start to fall out of the sky.)
That's the reason that the U.S. government won't move against robocallers: they are making money, so ipso facto they must be doing something right. If you move against the robocallers, that's the beginning of a slippery slope to questioning the idea that money is the ultimate quality metric, and that will completely undermine the foundation (such as it is) of the current power structure.