Phone numbers are just a liability:

- It is kind of expensive,

- You are forced to provide it to many official institutions,

- It is the default or mandatory insecure 2FA for many institutions,

- It always get leaked somewhere and is one of the most common/reliable identifier.

We still have them around governments and telcos love it and old people and scammers are its last users.

The cost is a feature. Kinda also the case with IPv4 addresses.