As a single guy I'm on the site and in the LS for a few reasons:
while "single" I'm not always flying solo. I have some single women friends who like to attend events with me, so swapping is still an option, provided there's some mutual interest all around
some couples (more than some would imagine) like adding a single man to the mix (echoed above by various posters), - I've met some really great couples I'm still friends with through the LS
I like hanging out with LS'ers and kinksters. While those are two different groups, there is some overlap of people across groups.
People like my rope work. I'm happy to share, let people try it out, etc.