Oh, gosh....so many reasons. Mad Cook hit on several for me.
I cook because I love food (good thing I'm a small person and burn calories easily).
I think it all started with family - my parents both worked and I usually got home before they did, so as a teen I started with spaghetti sauces, stews, Sunday morning breakfasts, and just started playing around with food. We had a garden and I remember thinking how beautiful and tasty the produce was, even as a little kid.
I remember my mom's dishes as well as my grandma's, and have always strived to be as good a cook as they were, in my eyes. I fall short of that, at least according to my memories.
I love making things that they used to make, and sharing them with my daughters so that the dishes and memories live on.
I cook because I don't like pre-packaged foods, but I do have them occasionally. As some have said, it's a creative outlet and I like creating things. I've had some real flops, lol, but there've been some good ones, too.
My cousin Diana and her late husband Paul had a cooking show on cable TV back in the 80's, called "The New Way Gourmet". LOL. They started out with cooking classes in their home, got the TV show, and went on to write several cookbooks. It was fun to watch them - I was glued to every show and was so inspired by their creativity and enthusiasm. Lots of fun.
I'm not a great cook, but I do love creating, even if it's only a fruit or veggie salad, with all those beautiful colors and textures. And here in CA that's what many of my dishes end up being, especially in summer. LOL.
I've really rambled on. This is a fun thread, and I've enjoyed reading everyone's stories!