Morality does not compress; it's not something you can learn just by looking at the (nonhuman) environment or by doing logic; if you want to get all the details correct, you have to look at human brains.

Why? Why can't you rewrite this as "complexity and morality"?

You may talk about the difference between mathematical and moral insights. Which is true, but then mathematical insights aren't sufficient for intelligence. Maths doesn't tell you whether a snake is poisonous and will kill you or not....