Unsurprisingly: telcos sell outbound dialing capabilities to business customers.

For spam mitigations to work, the cost of selling that business must exceed its revenue.

Some, and I won't mention AT&T by name, are very curiously opposed to any regulations touching this.

I don’t seem to be charged for Scam Shield on my account. I’ve had one unknown number call and not leave a message over the last month, which is a far cry from the 20–40 spam calls per day some people report.