The scale isn’t a problem if you also have Meta’s profit margins. But most businesses don’t…

I don't think Meta's margins have something to do with this. Companies smaller in scale than Meta also have less data!

And yes, Scuba is in-memory, but it's not the requirement. Check this video out on how Honeycomb implemented their columnar storage: https://vimeo.com/331143124

That's what I don't understand about observability services.

They complicate things so much that it's sometimes more expensive to observe than to RUN the infra being observed.

Sounds like an unaligned incentives issue. Or maybe after a certain scale observing becomes cheaper than running?