The CSVs and Excel sheets thing is out of control. Basically the entire telecom infrastructure runs off assorted attachments sent to people with essentially zero verification. (I have a sinking suspicion that many other industries might run the same way.)

To govern which calling party number can get sent, you'd need an access control system that goes all the way down to the end user. For instance, if I start using Skype, I may want to place calls from Skype using my cell phone number. It's not desirable to block such usage.

Which means I'd have to have a way to make ABC Comm (who I bought my number from) signal their provider to signal their provider that I've now granted access to Skype. And this would be required every step of the way (ABC Comm would need to let everyone know which 5 providers they use. Each one of those providers would need to let everyone know which 20 providers they use, etc.)

So it's not really a lack of care or time. It's just that to make it work like you want it to actually work, you end up with this massively layered, complicated thing. And if any part goes wrong, you end up messing up people's calls. (And some of those calls could be 9-1-1 emergency calls, so you might end up killing someone.) All for what benefit, exactly?

The FCC could fix this problem overnight. They just need to levy fines, get serious about it. If I was liable for my customer's behaviour, I'd make them put up a deposit or go through some serious hoops - maybe require insurance. The entire problem would be solved within weeks. It'd just take a few hours of work in drafting the law to make sure good-faith actors aren't going to get hurt.