Have seen posts about why AI doesn't do walls, but no castles?

I have seen many posts online about how AI never builds walls, due to the sheer complexity and the AI potentially walling themselves in, but I've started playing again with some friends after a long hiatus and have noticed that the newer AI doesn't build castles often. I vaguely remember the old AI building multiple castles, but I have yet to see the new AI build more than one. Sometimes they also never build a market on maps with even a little water. Anyone know how to give them a little push?

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Side note: I've also noticed the AI tends to mass cheaper units as well. Such as Light Cavalry, Pikeman, etc.