You want fun? Try a trike! I've never had so much fun (and no, not one of those old man tricycles.)
The real reasons (in no particular order):
10. I'm a professional and have to wear a suit and tie (or pantyhose and heels)
9. No safe place to lock my bike up/they won't let me bring the bike inside the office
8. I live too far from work
7. I have to take the kids to/pick the kids up from school/soccer
6. No showers at work
5. Helmet hair
4. I need to run errands at lunch
3. It's too cold/hot outside
2. I just don't have the will power/can't get up early enough
1. It's not safe
These are real reasons people don't ride. It's not all about stereotypes of the gun-toting, fat, lazy, Chevy-drivin' American.