Even if there are no problems with github PRs in themselves, the tmux developers will certainly have an established workflow for reviewing patches and applying

Even if there are no problems with github PRs in themselves, the tmux developers will certainly have an established workflow for reviewing patches and applying them. The last thing they want to do while they're migrating from one hosting site to another is to upend their entirely functional code review workflow when that's not the thing that's broken and forcing the migration...