What specific property of git mandates a website to not clean up those dangling commits?

Git has no de jure hierarchy of repositories. We de facto treat the GH repo as the primary one (and call it "origin"), but mechanically it's a peer repo. Even though it lets other repos push it around a bit and obeys commands like "change the branch to point to another commit", there are no commands to force it to delete the data.

	▲	eviks a day ago \| parent [-]
		> Even though it lets other repos push it around So there is hierarchy > there are no commands to force it to delete the data. That's just the current state, the question was how git prevents "de facto" deletion on a server? How is it anti-git to ask the server to execute git garbage collection commands, for example?