This makes me think of how I get a notification for every spam text message. It's the most enraging thing. I'd rather just get the spam text and ignore it myself than get a notification that I got a spam text and have to ignore or read it.
My point is - once upon a time Google had the confidence to develop features. Imagine getting a notification every time your Gmail gets spammed. You don't because Google is confident they can detect spam. I'm still getting spam text notifications on my Android because Google isn't confident and I think that's the same reason they haven't already solved unknown callers.