This is or was part of their anti-spam/flooding protection.
That's the official explanation. A phone number is a nice way to attach a real world identity to the data (which of course is sold to advertisers/data brokers etc).
Wayland has at least one deal breaker for me. It doesn't remember where my windows were at logout when saving the session. I have six virtual desktops and have specific windows in certain desktops. Putting everything back where they belong after each login, no thank you. Until they add that I'll stick to X11.
LibreWolf