What stops you from changing the service and suggesting same thing to your friends and family? There are alternatives around

I do use Signal. But unfortunately I lack convincing power to make everyone else use Signal.

But this is not about alternatives to WhatsApp, imo it's weird that this even happens/is possible.

What do you expect from Facebook? They make their money with advertising, of course they will exploit and capitalize everything that gets send through their channels.

I expect that they don't lie on their public website. This is what WhatsApp says on their own website https://faq.whatsapp.com/general/security-and-privacy/answer... :

  Neither WhatsApp nor Facebook can read your messages or hear your calls with your friends, family, and co-workers on WhatsApp. Whatever you share, it stays between you. That’s because your personal messages are protected by end-to-end encryption. We will never weaken this security and we clearly label each chat so you know our commitment.

Well they also promised to never exchange data between WhatsApp and Facebook when they bought WhatsApp. You simply can't believe any promise Facebook (or any FAANG company for that matter) makes regarding privacy or how they protect your personal data.

> it's weird that this even happens/is possible.

It’s not. This will happen with any chat app that is locked to a single service. Stop using those.

It's weird if even WhatsApp says it's not possible (see my other comment).

Are you sure you didn't see any ads about backpacks before?

Yes, I'm sure, not even camping related ads. I'm a hotel guy.

Smartphone chat apps are not secure. Smartphones apps are much more like web pages than desktop apps and should be treated like web pages.

If you have a secret to keep don’t share it with a phone.

There are plenty of secure alternatives to WhatsApp (Threema, Signal, Matrix just to name a few)

WhatsApp used to be one of those and it changed. With the exception of matrix there’s nothing to stop the same thing from happening with the others.

TL/TR: stop using WhatsApp