Why can't I just pay FB to opt out of WhatsApp's data collection?

You may find out just how much your data is worth on the market. I’d love to see the option of a subscription in more places, like FB itself. They’d still be serving ads and making money off that.

Their costs would go up, they may balk at that, but I expect it’s trivial given their profitability. Wonder how they’d price “private-mode” properties.

More importantly: do you trust FB to stop selling your data when they take your money?

I would also prefer to pay a fee for Gmail, Whatsapp etc so we don't need to participate in the advertising as a revenue model.

There are a lot of people who can't pay for the service (the next billion users). Would you be OK with paying a bit more to cover their use?

I too agree with this angle.