Re: it's part of the the SATA specification.
"But (1) why, on physically identical connectors, did someone decide to make it active high?"
Because Google, Amazon, ect had been cheaping out with their custom back planes for years, because the 3.3v pin wasn't used by HDDs they decided to not bother including it on their backplanes. So when they decided to use that pin for remote shutdown they were faced with the option of either making the drivers not work in their old servers or in consumers old computers (which did supply the 3.3v), so they chose to make it the consumers issue.
Biting the hand that feeds IT
