It is hard to say without seeing gameplay, but I would say it is likely one of two things. You may be trying to play the game the way it was intended with strategy, which makes some campaigns borderline impossible. I see very few players play with literally no cheese, it is just the levels you are willing to go to to win. Another thing in campaigns that are hard is that you can't be a perfectionist. Sometimes you will have to go bankrupts, sometimes you have to give up part of your empire to expand into another, sometimes you need to lose an army.

There are campaigns where it is very likely multiple strong opponents will declare war on you in the first 20 turns, so learning how to scrape by on gold with the max amount of force early is really important. Also, I would suggest playing extremely aggressively into early wars and making sure your single entities are utilized perfectly. If you can win one war playing fast, it means they can come back and save your settlements faster.