Maybe it's one reason WhatsApp is now encouraging "usernames" in lieu of phone numbers

Remove/hide contact information so that users cannot easily contact each other without going through the third party, Meta

Facebook did this many years ago

For example, imagine the user knows WhatsApp is going offline or the user gets tired using of WhatsApp

If the user can easily extract or save a list of her contacts' phone numbers then the user can maintain contact with them without WhatsApp

Otherwise the user may believe leaving WhatsApp would mean the user would lose touch with some/all the user's WhatsApp contacts