There is absolutely no reason to force phone numbers, they could add the option of username/email. Except for surveillance of KYCed numbers for social graph building.
Discussion
How about another pub key / private key setup like #nostr ?
I always looked at it like an iMessage for everyone kind of trade off they made. It was simple enough and familiar enough to gain popularity. Never thought of it being used with anyone you wouldn't want to share your number with.
Has anyone ever told that you are like ChatGPT personified? Everything you say, you say it with 100% conviction 😅