But I also think that if a maintainer asks you to jump before submitting a PR, you politely ask, “how high?”
You might argue that by making rules, even futile ones, you at least establish expectations and take a moral stance. Well, you can make a statement without dressing it up as a rule. But you don't get to be sanctimonious that way I guess.
Not every time, but sometimes. The threat of being caught isn't meaningless. You can decide not to play in someone else's walled garden if you want but the least you can do is respect their rules, bare minimum of human decency.