Firstly, I'm really glad you're enjoying it! It's becoming very clear to me that I need to clarify the rules, and add a tutorial mode, but to help you out I thought I would go through why those 8 villages that were lost.
Villages A, B and C only have "access" to 2 corn tiles, they need one each for a total of 3 to survive. By access I mean, in an area not divided by forest. Village D is isolated by surrounding forest so it has no access to corn or any other villages.
Villages E, F, G and H only has access to 2 corn tiles. I hope this helps!