Vendor lock in. I will not touch any IM services that is not completly open (client and server) and federated. I am looking for matrix.org that uses Olm [1] for E2E encryption.
The only reason why Facebook has as much power as it does is because of user lock-in, but that use lock-in is only strong because no one fights it actively.
Therefore, I started evangelising from WhatsApp to Telegram
Telegram is also a close silo. Tell your friend to use programs that use an open protocol like XMPP [1].
https://www.youtube.com/watch?v=_-RSravgi_Y