I always give people a way to test this themselves.
Those ads you see? They're not random. If you're a gamer, for example, and you often talk about gaming, there's a reason your ads reflect that.
WhatsApp is free because you are the product. And even if you're paying for the business version — you're still the product.
There's too much money to be made for you not to be the product. And there's too much legal liability for us to turn a blind eye to what's happening on the network. So even if there were no profit in it (and there is), we'd still be watching — because we have to.