The only valid reasons for the latter are (1) to collect your PII and/or (2) because they think that they know better than you and they're going to force you to do a thing because they think it's in your best interests - in other words, a tyrant ruling over a techno-feudalistic society.
If Google was really concerned only for the safety of their users, and not trying to obtain PII for their personal use, they would build an opt-out button, something that would allow users to print out a one-time-use password/encryption key, or register an alternate email address, in lieu of providing a phone number. They don't.
Your explanation doesn't hold water.