_Mohammed_ saidI think it is because females tend to be more vocal in expressing their feelings naturally.
Men tend to not talk as often as females and one could make a very big assumption that it correlates to why they don't moan as frequently in bed.
I could be wrong.
It is part nature and part society. Humans, by design, are not monogamous creatures. Humans become turned on when they see and hear a receptive partner. We have all sorts of neat biological gadgets for having sex with multiple partners. Our penis, for example, is designed like a piston to pump out semen from a hole with the flanged head. Females have a sexual response that calls to other mates, hoping for a preferred one. (which, by the way, is not saying that individual females may actually want multiple partners).
So, there is this underlying sexual response coupled with social expectations for female sexual behavior. Males want to feel like they are the alpha male and that they are the best at giving them pleasure. So we reinforce those base line sexual responses to the point that we get what you see in porn: that clownish, over the top fantasy of real sex.
You experience, Mr,Mohammed, also has society cutting into biology. Men grunt and growl during sex. We are showing the rest of the group that we are top dog and fucking her so god damn good. But gay men, there is a degree of shame. We become silent during sex to hide it. It doesn't have to be like porn, where we say silly things like "oh god yeah. Fuck that hole. Fuck it. You like fucking that hole. Oh yeah. Fuck it!" But a little vocal response to let everyone know that everyone is having a good time is nice.