Even though Git is decentralised, people like having a simple client-server model for version control. So with Github being the most funded free Git hosting service it grew to being the biggest. They also built out the extra services on top of git hosting, the issue tracker, CI/CD, discussion board, integrated wiki, github-pages, etc.

I would say all of those things were present before the acquisition, enough that Microsoft itself started to use the site for its own open source code hosting.

If you travel back to 2018 and ask random software engineers "are git and github developed and owned by the same company", a fair number of them would say yes, just like today.

> Was GitHub really critical at time of purchase?

Do you think they would have bought it otherwise? Same for NPM, they got bought for huge sums of money because they were "critical" already.

It was the leading git storage at the time of acquisition, for many people synonymous with git itself