On top of dabinat's point on consent, there is the resource use and accuracy part.

I can't imagine how much sleuthing is needed to infer who would be someone's divorced mother if it wasn't explicitely labelled, but it's completely unneeded until the day they actually try to use that info through some Apple service. Then, they'll be in for a surprise the day it infers it's their boss instead.

That's the other side of whimsy and "magic".