I think a huge part of it was that I thought it was very stressful to not only pick meals but to also write down all of the ingredients, figure out what I did or didn't have, and then go shopping. Planning my meals was making my life stressful and complicated, rather than simple like it promised.
I'm a pretty avid reading of Feeding the Soil. It's a great little blog about a family that's trying to get the most out of life while spending the least amount of money, and helping their community grow in the process. I don't always agree with everything, but I love some of the ideas she has. She recently posted a meal plan grocery list that her and her husband set up, and it clicked with me.
(my grocery sheet)
Seriously. If you're struggling with meal planning, this is totally worth a shot.