Ask HN: Why don't more companies self-host repositories?

Most companies have an organization on Github and use it for their public SDKs, API wrappers, etc.

These companies tend to not take pull requests or anything, so there's little social interaction. Why don't most of these companies self host read only repositories for these SDKs?

It seems like they add a dependency (Github) for little gain (maybe some SEO link juice and the rare issue that gets reported).