If someone tells you that it's impossible to trace the origins of spam, ask yourself how they can know whom to bill.
The reality is that it's possible and easy but only when the bottom-line is concerned.
It needs to make business sense to prevent spam/scams by there being penalties for screwing things up, and incentives for doing well. Otherwise you're right, unscrupulous telco companies like to make money by charging scammers to send messages to customers.
Currently that's not the case, so the excuse of not being able to trace the source of the spam is successfully preempting regulation as nobody involved has the skills and/or financial incentives to ask "hold on, how come you know who to bill but not who's originating the spam?".
Simpler explanation is that the phone companies don't care about the scams because it doesn't affect them. They aren't liable, and there is no mechanism to report scams to them, and make them spend money investigating.