What I find amusing is that all of those WhatsApp users don't know or don't care that they are uploading their entire list of contacts (with phone numbers) to Meta/Facebook and syncing it every day.

That "end-to-end encrypted" advertising has done its job, and most people don't want to be bothered with thinking too much anyway.

WhatsApp is a gold mine of real-world social graph data for Facebook/Meta. If you think for a moment how much you can infer by merging that data with other information you get from people using other FB apps and sites, it's incredible.