You say BitBucket and Gitlab are alternatives, but at the same time you can not fathom the idea of migrating away from GitHub. So it's safe to say that GitHub has a de facto control of the market, much like Windows controlled the desktop market until early 2000's.
I can fathom a migration. It's just not pretty & is expensive. The experience coming out of source forge was not pleasant, and that was before the project even had a CI/CD. The early days of Github were game changers for FOSS, no more consolidating email patches together, etc.. So, this goes to whether Github still has a reputation and a brand for being a good home to FOSS. The argument that copilot, which automates what is otherwise an available and a manual process, and lifts just lines of code and small sections - is not at all "reproducing software". It's like someone used the "pad left" functionality from someones Javascript on their web page. Being able to do that is part of the point, it is a feature of openness, it's not a corporate back-door, market monopoly enabling flaw.
I'm curious if anyone can find references, though when I researched market share of code hosting companies a few years ago (for a private company that was moving off of BitBucket), it turned out that there were more private companies on Gitlab than Github. Github though had a big advantage for hosting FOSS. We wound up moving to Microsoft Azure because the scrum boards and Microsoft integration were appealing and familiar to the company. I don't see it being analagous as Windows desktop control in the early 2000's.
