Except you might not want some kloud-krap outside company storing sensitive faxes for you. To provide stable Internet, one needs some sort of wiring to premises. They can provide POTS over that at virtually no cost, doesn’t have to be a traditional twisted pair.

But if ones use a separate channel for POTS vs Internet which gets priority, it does away with any latency or QoS issues that VoIP has. Example: Verizon FiOS. It’s POTS over fiber, not VoIP since voice doesn’t use an IP network.