There are many noble reasons to run: to inspire children, to channel addictive tendencies, to raise money for charity. The running community is filled with amazing people who work to make the world a better place.
My reasons are a little less dignified. I run because I'm hungry, and I run because I'm vain.
I love to eat. I have no allergies and a diverse palate, so literally everything sounds delicious all the time. Now I could eat hamburgers and tacos without running so much (this is America after all), but then my second motivator comes into play. Since I don't want to weight 300 pounds, I work to strike a balance between calories in and calories out.
This morning I ran eight miles, and promptly followed them up with a hamburger. I have no regrets about my day.
I use running to supplement my life. Some days it's an hour of reflection, some days a cathartic release, and some days just a good old fashioned calorie buffer. Training can be grueling, so any type of motivation helps. I wish I were motivated solely by splits and PRs, but I'm not. A meal just tastes so much sweeter when it's earned. Bon appetit!