>>I just have to wonder who green-lit this idea to begin with.

I suspect, with no inside knowledge, that there's someone high up in Apple who feels very, very passionately about child abuse/these sorts of images due to some personal connection, and they are championing the idea internally. And tbh not the worst bugbear to have, but obviously this isn't the way to address it.

As for why the big players aren't jumping on this - it's a tricky line to walk, you don't ever want to be seen as pro child abuse.