Because it's easy to do SIM swam scams, spoof phone numbers, etc. It's another personally-identifying bit of information that we shouldn't need for authentication.
As attacks become more efficient, we're moving to better solutions like YubiKeys and TOTP-based authenticator apps. Both of which are still fairly easy to use.
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.