>At the same time, the larger tech companies (Meta and Google, specifically) ended up building off of hg and not git because (at the time, especially) git cannot scale up to their use cases.

Fun story: I don't really know what Microsoft's server-side infra looked like when they migrated the OS repo to git (which, contrary to the name, contains more than just stuff related to the Windows OS), but after a few years they started to hit some object scaling limitations where the easiest solution was to just freeze the "os" repo and roll everyone over to "os2".