It's biology...basically. Of course cultural influences may affect the expression of the sexuality, but basic sexuality comes hardwired with one's genetic and epigenetic factors. Biologically, the function of humans is to live and to reproduce. Biologically, a woman's function is to produce the kids, and thus, women's biology is geared toward choosing a good mate and raising the resulting child(ren). (Given the divorce rate, it appears modern women are not particularly adept at this choosing skill!) Biologically, a man's function is to inseminate as many women as he can, and thus men's biology is geared toward maximum horniness. Of course, there can and are going to be significant variations in any one individual—that is not the point when looking to determine the operative biological generalization.
Of course there are cultural and social and religious factors involved, but these don't alter that which comes hard wired at the root level; they only may influence its expression. So, yes, two guys may see the efficacy of sex whenever and be able to act on it much more easily than can a heterosexual guy. It doesn't mean the urge is any different, just that its opportunity for expression may be less amongst heterosexual males.