I've asked around in my circles, because I am genuinely interested: Everyone not working in startup space IS hosting their own instances.

Hell, even I do it.

Where I work we're hosting our own gitlab instance and the previous company I worked for hosted their own Bitbucket. For most developers I know it's either a self hosted git platform instance or Github enterprise.

Even my faculty, which otherwise licks Microsoft’s boots at all opportunities, uses self-hosted GitLab.

I am working for small companies, for medium sized companies and for huge behemoths.

None (apart from one customer as I said) has their code on GitHub.

The big ones because of trade secrets. Which is ironic, because most of them use Microsoft Teams and talk freely there xD