Surely a bigger question is how a site with a basis in PHP transformed to making PHP compilers, .js frameworks, Haskell, C++ etc.

They seemed to have succeeded in creating a culture of coders/hackers that were opinionated/empowered sufficiently to use their tool of choice, and to persuade others of the advantages.

This doesn't really happen in large-cap companies (though does happen to empowered teams, but even then, only somewhat - thinking finance). And speaks to advantages.