Why do you care? Your messages are still E2E-encrypted, those won't show ads. Why do you care if you see a promoted channel once in a while or during status updates? I see a bunch of random s**t all the time on those, anyway, so I really don't pay attention.
So, do you expect to be given something in exchange for nothing? They answer to shareholders, and I'm sure they want to see WhatsApp generating revenue in some way. We'd do the exact same thing, come on...
You see ads on everything because you don't want to pay them money. YouTube, Facebook, Instagram, Netflix, Google Search, Reddit, everything follows the same economics, why are they different?