It’s a given that the more GitHub features you use, the more difficult it is to move away from GitHub. It’s also a given that you can reasonably limit the extent to which you use GitHub and thereby limit the difficulty in transitioning to another solution.
The idea that it’s GitHub locking you in rather than you locking yourself in to GitHub is the argument I take issue with. But no quarrel at all with Gnome choosing GitLab, because GitLab is genuinely great.
The whole reason GNOME wanted to switch is because they wanted to have all the extra features (issues, etc) in a single place, as is provided by Github and Gitlab. Their old cgit interface already did a good job at hosting their git repositories.
The idea that it’s GitHub locking you in rather than you locking yourself in to GitHub is the argument I take issue with. But no quarrel at all with Gnome choosing GitLab, because GitLab is genuinely great.