Of course, but I can guarantee Facebook has run the numbers. They are currently doing what makes them the most money. That happens to be ads.

The user data they sell to advertisers has a lot to do with your social network. Who you know, what their interests are, who they know, etc.

For Facebook to allow individuals to pay to opt out of their data being sold, it affects more than just that individual's data. I.e. it affects all their friends and friends-of-friends data.

I expect that the only way Facebook would be able to offer a pay-to-opt-out plan would be for everyone on Facebook to start doing, which would never work and they would never attempt.

I imagine the most we'll see in this direction is some sort of half-assed attempt where they offer to let you pay them money to stop some tracking, but still continue to most of it anyway.