The mid-20th century USA ended up developing a fairly extensive body of case law about the phone system along those lines. Once upon a time, quite a few people did think it was the phone company's responsibility to prevent such calls, within reason. And they litigated the question.

Does the phone company has the right to disconnect abusive and profane callers? Does the phone company have an obligation to disconnect such users? If the phone company fails to do so, are they civilly liable? Given the government-regulated quasi-monopoly status of the Bell system, was there a First Amendment or due process angle, if the phone company disconnects users for placing obscene or offensive calls?

The answers to such questions were not particularly obvious and it just sort of evolved organically to the status quo today. In some cases new laws were passed to deal with the situation, such as one that makes it a federal offence to knowingly place an obscene and unwanted phone call to someone. Similarly, there are a number of regulations that impose an obligation on the carriers to try to reduce spam, unwanted solicitation, maintain calling logs, etc.