Anatomy and diagnosis were done by studying what Galen said, and when what he said didn't fit the facts, physicians redoubled their efforts to figure out what he really meant. For all those centuries, medicine was not a science, but a branch of philology. Such foot-dragging was important in delaying the science of our human mind. But the main reason for this science's late arrival on the stage of human inquiry is that the brain and the mind are extremely complex. That three pound mass in your skull dwarfs in complexity such things as the sun, the solar system, Andromeda, the Virgo cluster . . .
Biology is closer to being in the same league as the sciences of the mind.
But I don't believe it. We know more about the Amazon rain forest than we do our minds. I mean, we have whole, deep theories of the rain forest, which use the theory of evolution as a basis. We have nothing comparable for the mind and brain. We know lots and lots of facts about mind and brain, we have hundreds of little proto-theories about its various aspects, properties, and processes.