Basically ML has made such significant practical advances--in no small part on the back of Moore's Law, large datasets, and specialized processors--that we've largely punted on (non-academic) attempts to bring forward cognitive science and the like on which there really hasn't been great progress decades on. Some of the same neurophysiology debates that were happening when. I was an undergrad in the late 70s still seem to be happening in not much different form.
But it's reasonable to ask whether there's some point beyond ML can't take you. Peter Norvig I think made a comment to the effect of "We have been making great progress--all the way to the top of the tree."
