>GitHub had over 14,000 repositories.

I'm surprised the idea of reducing the number of repositories wasn't floated. Having extremely big cardinality, 1 github repo to 14,000 repositories you are going to struggle with ownership compared to an organization owning a few folders within a repository and those folders hold multiple projects. This feeling of closeness to other projects makes ownership feel more natural than where a repository feels like it's out in the middle of nowhere.

It's easier to assign ownership to a single directory than having to track it for n possible projects within it.