I get all the privacy concerns, but this was actually super useful for people who opted-in. Manually retyping everybody's name when tagging them in 50 photos from an event is torturous.
I always figured this constraint was kept as a happy convenience so that Facebook have a steady supply of training data for their face recognition service.
If they are shutting that service down, maybe they'll let us tag albums?
It was one of those "by continuing to use our service(s), you are opting-in" t&C's updates.
So in short: nobody did but legally there is a box ticked.
I guess it could just be used to annotate images, or to recall who's who for your own use, a la how people used to write everyone's names on the back of photos.