Maybe someone's finally solved it over the past few years, but he was telling me that automating apple harvests was still a massive challenge about 5 years ago - there are/were machines to pick up fallen apples and robots for picking them individually, but you can't easily shake all the apples off a mature tree for collection and a human can pick them from the branch far more quickly than a robot. From what I can see online there's one that does it for young trees, but most of them are still glorified cherry-pickers.