Plus even a flowchart of the ideal strategy is hard to create without using black boxes or brute-force iterating every possible proof of something.

EDIT: Oh, and the humans played to win a game different from the nominal game. That distinction is important, because you can only observe them in the actual game and not the nominal one. (At CFAR workshops, PD for low stakes resulted in universal cooperation when it was done openly; the first time it was done semi-anonymously, there was a defector. There were several other differences as well, but the nominal stakes were similar.)