Why are WhatsApp, Telegram and similar apps deemed as unsafe from a privacy standpoint?

I am asking to learn, not to challenge r/privacy -

How come apps like Whatsapp can claim they are completely encrypted and explicitly claim that they can't even read your conversations or access your backups,

But then be deemed as unsafe and invasive of privacy?

Isn't it false advertising if that is the case ?

If they can't read or access your messages, they shouldn't be able to scan them for data and use for advertising, or even give to …

access advertising aid apps asking backups case challenge claim conversations data encrypted investigation isn learn messages police privacy scan telegram whatsapp