You're conflating GitHub the platform with GitHub the bundle of services. CI is optional, swappable, not unique to GitHub. Sponsorship infrastructure and discoverability are not. The complaints target the optional layer. The migration sacrifices the sticky layer. That's backwards, and ironic, with the intention of being performative. It's almost like selling your car because a tire lost some air, lol.
If they had trouble with Git on GitHub, and then left GitHub for Codeberg, where they also have to use Git, then that would be very strange.
Instead, they had trouble with GitHub, so they left GitHub, which makes perfect sense.