The advantage is the government is the one liable for it working. Right now, I’m at the mercy of ATT/Verizon/T-Mobile keeping my phone number working for identification purposes. And they have no legal mandate to continue doing that, and I have no recourse if they stop doing that for whatever reason.

It is all the same reasons the government does not outsource issuing of passports. It needs to be from an official source with legal protections.