I've been repeating with one lady for a year and a half. And that's for twice a week for the last year.
The first time I repeated to be polite. I didn't have a great time, but she'd given me her number and I told her I'd call so I thought it would be rude if I didn't.
After that I repeated because the sex was great and she had a fun personality.
Then I was repeating because the sex was still great and we started going out and doing things and getting to know eachother better.
Then I was repeating because even though the sex wasn't as good we were forming stronger bonds on a personal level, found out that we shared some common interests and she has a way of making me feel great when I'm with her.
Lately the sex has been rare (but that trend should be reversing very shortly), but she still makes me feel great and we're very good friends. I also repeat now because I'm so darned attached to her.
I guess the reasons you repeat can change.