With big decisions, you don't get the option of just not deciding. And more often than not, you don't get much time to make them, or at least not as much as you'd like. The consequences may be difficult, or even devastating, but having the decisions themselves be difficult is a luxury. When it's life and death, you can't dither. You make a choice and you pray to Andraste that it works out. When the results don't matter, that's when you can sit around and contemplate and do some research and ask for more information.
So it's not really that the little decisions are actually harder, I suppose, and more just that I never had time to let the big decisions be hard.