Why can't Telco's tag Internet calls?

Why can't AT&T validate a number before it passes on the call?  Even calls from the Internet have to gain access the public service telephone network (PSTN) at some point.  That Telco needs to validate a number or it should be fined.  I get about five to ten calls per day from random spoofed numbers (I just got one while typing this).  AT&T states that they 'can't do anything about it'.  That's not true.  If AT&T provides a PRI to a business, they should enforce the DID tagging and not give that flexibility to the business that is buying it.

Yes, folks have suggested that I just 'change my number', but I don't feel I should have to do that.  I've had that number with AT&T for over 20 years.  Isn't that worth something to AT&T?