I'm not a cuddler most of the time. We cuddle all night and sleep all spooned up. And we snuggle on the couch. After lovin' I'm usually just worn out and want to be left alone to crash.
I believe that the male brain after orgasm releases more serotonin (melatonin? whatever). Therefor while some women get sleepy, most men do.
In my particular case, we're never starting 'til after 10:30ish, so when I'm done, I'm done.