If Facebook was going to exploit Whatsapp or similar to make money btw (other than putting in regular ads, sponsored posts, and business accounts), they probably wouldn't directly break the E2EE, they would mine the metadata, which they're already marketing as a tool for "fighting abuse".

Then, they could sell the idea of protecting the confidentiality of your messages. In a chat called puppies? Alright, so we know you like puppies. Didn't break the E2EE.