Supply and Demand.
It's obvious that hot, good guys are in high demand. The ones that prefer to be single most likely have been screwed in the past and want to make sure that when they date someone, that it's someone worth investing time in and not get screwed over. The ones that just want to fool around, perhaps they want to enjoy the bachelor life for awhile before getting hitched, either that or they had a recent break-up.
I'm sure most of the good ones are taken though. I mean, if he's a hot, good guy, why would their significant other want to let them go? That's assuming the significant other isn't crazy. And if they're both hot, good guys, well, you're pretty much out of luck there.
Anyways, it's better to look for the good guys, not necessarily hot. It's always possible for them to build a smoking body y'know.