We use programming languages like C to create complex branching algorithms that are turned a linear machine code tape. Programmers generally can not understand assembly even if they understand the branching code that is turned into assembly. Even if assembly had variables, just the fact that if/else's and function calls are turned into jumps is enough to make the code too complicated to understand. It might be possible to disassemble back to C by resolving the jumps into something that is easier to understand.
Imagine if brains worked the same way. That there is actually a naturally-forming high level "brain language" that is turned by a "brain compiler" function into a low-level "brain assembly," but when we look at it all we see is the assembly. That what the brain is actually doing is relatively simple, but because we can only observe the output of the compiler function it appears to be insanely complex to reverse-engineer.
Then again, I don't have the faintest idea of how brains work either.