[kyrra]

(googler, opinions are my own)

Google interestingly also still contributes to mercurial[0], but I don't think has said why externally officially.

But yes, my understanding is that mercurial is much easier to replace parts of the flow without entirely hacking the codebase to bits. Microsoft's solution for git required them to fork the code base, which I still don't think has been fully merged with upstream yet? And as others said, the mercurial community was more open to enterprise contributing things than git can be.

https://www.mercurial-scm.org/wiki/5.2sprint