Not enough demands? Are you serious? Sometimes they seem to make demands every 5 turns. If that's not enough then I don't know what is.
Perhaps they should respond more hostile towards an demand that is turned down.
But the entire system is unsatisfactory imho. The AI treats you entirely differently as it treats other AIs. That's bad design imho. It's a quick way of making the game more difficult, but it's also dirty.
If the AI blackmails me, ok, fine, but then I want it to blackmail other AIs as well. And if other AIs cave in to blackmail from others, then I want them to cave in from demands from me as well. Same with tech trading, they always demand ridiculous lobsided deals, but when I demand such a deal they always refuse. The logical result is that AIs will never trade amongst eachother, each party wanting a deal that is unacceptable for the other. However, the AI does trade among eachother, all the time.
Ideally, I want the AI to see no difference at all between me and other AIs.
This would make the game easier of course. So then either the AI has to become smarter, or has to get more bonusses.
Aggresive AIs should, imho, be a lot more opportunistic, striking whoever is weak. Right now they are often completely suicidal in wars. Loosing 4 wars in a row against me and then declaring a 5th. It's okay if they hold grudges against someone who attacked them. But it's not me starting those wars.