Any barrier to abuse makes abuse harder.

Not really lol, literally if you add a robots.txt check someone can just create a fork repo with a git action that escapes that routine every time the original is pushed... Adding options for filter and respecting things is great even as defaults, but trying to force "good behavior" tends to just lead to people setting up a workaround that everyone eventually uses because why use the hamstrung version instead of the open version and make your own choices.