Most users care about the enjoyment/utility/stimulation they get out of a social network. Some users care about their privacy. Needing an extra $30-60/year does not rank high on user priorities.
While facebook might make $200/US individual, their profit margin is only 30%.
Let's say every user gets 10% of the average, or $20/year. As you say, not a big priority. But some people would sign up, who otherwise would not. And some people would keep their accounts, who otherwise would not. Win for Facebook? Hard to say.
Now, what if Facebook gave each person 10% of what they personally brought in? That wouldn't take much more tracking than what they already do. But in this case, you'd have a lot of people maximizing their time on Facebook in order to increase their payout. Win for them, bigger win for Facebook. Heck, Facebook could even get rid of all their stupid dark patterns, and stop the endless research into more dark patterns, improving their bottom line even more. No need to trick people into engaging if they are voluntarily engaging for a small sum.
I still don't think the ROI for the user is there. The average FB user spends about 35 min per day, or 210hrs/year on the platform. Assuming 10% revenue sharing, that is $0.10/hour. If the average user were to double their time on the platform, they would make an extra $20/year.
This is a laughable incentive for most people, let alone your most valuable add targets (people with disposable income).
They sort of do. The money is converted into the utility of the product to each user. Technically, they could lower the utility of Facebook and pay you the rest.