[marklar423]

I think Git was initially more popular and that had compounding effects that made it eclipse Mercurial.

In 2010 or so we tried to adopt Mercurial at the small company I worked at, but the support for Git was just so much better - even back then. Git's popularity meant that tooling, documentation, and general ease of finding people to ask questions was 100x easier with Git, so we switched. I'd imagine the same thing played out many times over.

A few FAANGs did and still use Mercurial, but they're on their own islands and don't really affect the wider tech ecosystem.

[010101010101]

Circa ~2007/8 they were both very much on equal footing as far as popularity with individual engineers goes. The Linux kernel being on Git gave it an allure to most that Mercurial never had, but it was GitHub’s ascendancy that really started to put distance between the two.