I was explaining this to my daughter in quite simplified terms the other day- we evolved to taste sugar and enjoy it because finding a sweet edible plant meant we had a source of energy to help us hunt that day. Pretty useful if you're a hunter-gatherer.
So we seek out sugar. Now we can get it whenever we want it, in much more massive quantities than we are supposed to be processing. Most of us are addicted. I'm not an exception.
Your sauce will still have less sugar than others, but if I understand correctly, simmering for hours will break down the more complex sugars in tomatoes into simpler sugars resulting in a somewhat sweeter taste
I think cooking does also dull the percieved acidity of food though, hence lemon juice or other acids often being added at the end so as to keep the brightness. But I'm not actually sure if the pH changes or if it's just a change in the tartness we associate with acidity, maybe someone can chime in with more information :)