Simply put it.. Here's a few reasons,
1. Ethical viewpoint and mindset.
2. Conservative thinking
3. He is saving the best for the wedding night
4. He is actually a she? or Gay? or something..
5. His pen is tiny and afraid you will laugh.
6. He may have kena STD and do not want to infect you.
7. He is too tired when you are asking.
8. He do not know how to enjoy sex.
9. He is too shy, you probably need to rape him.
10. He thinks that you are joking and doesn't take you
seriously.