At harder difficulty settings, the game is more generous to the AI (it's like they get to play on easy). So they have more money, happier citizens, etc., all the things you'd expect on easy.
This means that despite the inherent inability to *think*, the AI has lots of resources to throw around, and is far more likely to follow the orders that the modder designed, and less likely to 'get stuck' on some issue like being out of a given resource such as cash or casalon (easy mode, remember: easier to afford to mine what they need, easier to get quantities of it, easier to build ships to exploit it, etc.)
So, higher difficulty = AI's get more $, resources, etc., = they are able to take advantage of the "smarts" endowed by this mod.
^^^ my assumptions, could be wrong :P