[prebrov]

Compelling telcos to do that is the regulator's job.

Not sure about the US, but in most of the rest of the world regulators come up with new rules and regulations requiring some form of network upgrade all the time – SLAs, connectivity and routing requirements, legal interception, data residency, etc.

And telcos have no other way but to spend billions to protect some monopoly or enable more surveillance power for the governments. It's a matter of priorities, really.