I have the opposite view: the success of GitHub and the growth of code being open by default with everything running through git has probably brought more people into the git ecosystem than would have otherwise. I primarily use GitHub, but whenever I need something that I need to run myself I know I can fairly seamlessly switch over to something like GitLab.
For example, if GitHub ever started using a very proprietary application, I would just switch over to using regular git, and I'm guessing many others would too.