It is a common trope that gay men are more prone than other demographics to engage in frequent casual sex, which accurately reflects my own experience. This, I think, can be explained simply by the fact that for a gay man, the only barrier to having sex is another man's willingness to have sex with him, and since males are by far the sluttier of the two genders, this amounts to a very low barrier indeed. Thus, it's not the case that straight men aren't slutty, but rather that in most cases they are kept from being as slutty as they want to be due to the shortage of loose women willing to have a one-night stand.
Notice that gay males are the only ones who are both attracted to men (the sluttier and therefore easier-to-sleep-with gender) and male themselves (and therefore slutty themselves).
The intention of this post isn't to promote homophobia, but rather to offer an alternative explanation to the one typically used to explain gay promiscuity, namely one appealing to the "moral degeneracy" of gay culture and gays themselves.