1. 99.9% of my paying customers have a credit card <---this is #1 for a reason
2. I've only had ~3 customers ever complain about my lack of Paypal. I made a special arrangement for 1. She ended up canceling.
3. Paypal doesn't allow the custom flows (upsells, cross-sells) that I can do with my shopping cart
4. Paypal doesn't integrate as nicely with my backend analytics, and I prefer to have all my sales centralized
5. Hearing bad bad horror stories about Paypal is just another, distant reason why I feel no urge to use them
Hope this helps.