I feel the same and was happy to pay the $1 to WhatsApp, until that changed. I can only imagine that FB values its unfettered access to you and your data as worth more than $40 or double that!
A simple division doesn't tell the whole story, but gets us into ballpark territory, call it $20/user/year. It's probably something power-distribution-ish, with a few whales clicking on the most profitable scams and mesothelioma ads, and a long tail of people who are below average. Much like with what network TV actually makes per eyeball-second, it's actually shockingly easy to outbid advertisers.
One of the reasons I kinda look askance at the whole advertising ecosystem is precisely that it seems like nobody is even trying anything else despite the fact it seems like it ought to be a very swift and huge boost to Facebook's real revenues and stock price if they could convince people to give them $50/year. The obvious offer to me would be some sort of all-inclusive cloud storage service for photos or something, which, I mean, they're already doing. The fact that this seems to be unthinkable is what makes me start giving a bit more credence to the idea that there truly is some sort of ulterior motive at play here. Even just "here's $34.99 for the year, facebook, remove the damned ads! and now that you don't need it, stop tracking me" would probably make them a shitton of cash, even without any other changes like giving you back more control over your feed now that you've removed their incentives to manipulate it for their own advertising gain. Where's all that notorious capitalistic greed?
And suppose we were living in an alternate universe where that was an option... how different would the news stories of the past week look? There's non-monetary reasons for this too.
(Compare with Netflix, for instance. I pay them real money. They get lots of real preference data. It would totally be "monetizable" levels of detail. But there's basically nothing they could possibly do with that data that's worth more than the ~$150/year I give them, and trying to start stuffing ads in my face runs a marginal risk that I'll just leave that is probably not worth it. Maybe when Facebook first came out, subscriptions were out of the question, but they are clearly an option now.)
[1]: https://www.statista.com/statistics/277229/facebooks-annual-...
[2]: https://www.statista.com/statistics/264810/number-of-monthly...