[PvK]

Because the AI is not restricted in its designs by all of the same rules that a human player is. What the AI builds is determined by its design files, and its designs can be illegal in some ways. The only reason it doesn't cheat in the unmodded game is because its files are all legal in the unmodded game. If your mod introduces new restrictions, you may need to mod the AI files if you want the AI to obey the limits.

PvK