Sounds like a drop in the bucket for them.

That doesn't make a lot of sense though - Facebook generates revenue primarily from ad traffic (on all sorts of sites). It needs to be up for reputation and to harvest ever more detail for 'improving' those ads, sure, but not for revenue. (Modulo blip from ads on its own site.)

So you can't just divide over time like that.

What? It absolutely needs to be up -- those ads being served are on Facebook and Insta, not display banners on random sites.

That's what I meant by 'ads on its own site' - but I was under the impression that Facebook generated most revenue from selling data/ads for display elsewhere (as well as on Facebook.com itself, and other subsidiaries). Perhaps I was wrong about that? Quick search shows up 'audience network', but I'm not sure to what extent that's what I was thinking of.

Nope, for the most part all the ads that Facebook serves are for facebook owned sites and properties. They don't sell data, or have general ad placements on 3rd party websites.

wow...

It sounds like they are not even able to serve ads, on any property. So while far from perfect, it's probably a decent estimate without doing in-depth analysis.