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