Re: it's part of the the SATA specification.
Hm. Indeed. It was introduced as it was a feature in the SAS specifications. Most people kind of know the difference between buying a SAS drive and buying a SATA drive. During this transition period, which will be decades long, they'll have to learn to spot the difference between a SAS drive and two subtle flavours of SATA. So from two semi-incompatible standards, they've created three, two of which are wholly incompatible but are given the same name. But (1) why, on physically identical connectors, did someone decide to make it active high? and (2) why didn't WD/HGST put a jumper in so one could easily disconnect the pin from the 3.3V supply that the specification previously assigned to it and which most leads and backplanes for the last 20 years have been built to support?