Exactly my point. I'd venture to guess that Marriott (another hotel company that actually owns their properties and thus arguably has more at stake) has a tech stack vastly more complicated than Airbnb's, and yet Marriott would never announce they're building a "tech hub" in any city.

I think you are probably overestimating how enterprise does tech. Subcontracting, consultancies are the name of the game

For me at least, I found banking to be incredible, teams of DBAs managing very expensive database servers to perfection and high scale web apps that almost always work correctly

Such as?

moving billions of dollars daily with csv, tsv fixed-width files and sftp. /s

Petabytes upon petabytes, and it has to be correct, really well archived, and set up for reporting, stats, and ad hoc