You only believe that because you have chosen to believe it.

Take Facebook end-to-end encrypted messages for example. There are certain links it won't let you send, enough though it is supposedly E2EE. (I've seen it in situations like mentioning the piratebay domain name, which it tries to auto-preview and then fails. Hacking related websites as well I've seen the issue with.)

It likes to pretend it is a mysterious error, but if you immediately send a different link, it sends just fine. I don't use chat apps much these days, so I'm not sure if others see similar behavior, but I'd wager some do. Facebook is about the least trustworthy provider I'm likely to use, FWIW, so I expect a certain amount of smoke and mirrors from them.