The same way that an employee might only use GitHub on behalf of their employer. It's not mysterious or complicated. If my client brings me in to help on a software project that's already hosted on GitHub, that's what I have to use. So I use GitHub pretty much every workday, because I want to get paid. This is part of the problem: GitHub remains the default despite the fact that it is no good. Hence me writing the article, to try and change that.
Before I went independent I used GitHub for a bunch of different employers, so I've watched it's decline over the last decade from the front row.
My clients are the ones paying for GitHub enterprise, in this case. Depending on the context I'll either use my personal account or an account under their organization, etc. Usually I don't have admin permissions (rightfully!), sometimes I do.
I have used pretty much every corner of GitHub in pretty much every possible context for well over a decade. I'm sure you could find something I haven't touched, but you'd have to think pretty hard. I thought that would be obvious from the fact I talked about things like SLAs and GitHub actions, but I guess I should have been clearer.