It's not that they don't care, it's just that the protocol behind it was never designed for it.

Compared for example to email where when you want to send email to somebody, you discover its MX settings on the DNS level and then send it directly and the receiver can verify are you allowed to send those emails. With phone calls it's basically a network of interconnects so I'm sending the call directly to my provider but that provider to reach the destination has multiple steps and they have to trust each other with the numbers signalling. Compare it to a regular snail mail where everybody can write anything as a sender.

What most of the providers are switching to now is for enduser the case is if the phone number that you want to signal is not registered with us, you are not allowed to signal it. Which is fine and covers most of the cases but imagine that you are a business and have multiple providers And you have boughta number block with one provider and another one is offering you better minute price for outgoing calls. Or you want to have a forwarding to your cell phone number. Or you want to signal your number when you're calling prospects from CRM. The regulation usuall differs from country to country, but most allow you to signal any number that you own with any provider that you use. And this is correct, but the problem is verification.