This way you can improve your fruit classifier without needing to make changes to the general classifier. I think it also opens up the possibilities for things like having a general "offline" model on a smartphone but when connected to the internet it could make use of more specialised models.
It would also be cool if you could download offline models for things you're particularly interested in, like birds species etc.
I think one of the problems with having a really large AI that attempts to classify everything would be a sort of "tunnel vision" problem and eventually the AI has to make a guess as to what something is instead of saying "best I can do is this is an animal, but let me go ask a buddy of mine who's an expert on animals".