I wonder if this could be explained in a similar way to Hollywood movies. If the movies are designed to please the largest group of people, there is a greater chance people will choose to see it than another movie. The human law professors come with their own personalities, beliefs, and opinions that come through in their writing. An LLM has been trained to please the largest swathe of the population. That doesn't mean the answer is better; just like Captain America isn't necessarily better than American Beauty.