Let’s Talk About Sex, Baby!

Recently I read an essay about motherhood and sex, or rather, the complete (apparent) lack of sex after kids. Michelle and I have also discussed this situation when we?ve realised while talking to our girlfriends/acquaintances that there are a lot of couples who do not seem to be having sex on any sort of regular basis.
While I am not going to go into the intimate details of my own sex life, I will say this ? I?m getting some on a regular basis. I?m curious, why aren?t couples having sex? I know couples who are clearly very much in love, who have an obvious respect for each other that is apparent when they speak of their partner, but they aren?t having sex. Why? Is there a health reason? If you?re not having sex with your partner than how does that relationship differ than any other relationship you have with someone of the opposite sex? Isn?t the sex sort of what sets it apart? Does the mere fact that I even think that mean my own relationship is doomed to fail at some point?!
Obviously right after a baby is born the sex basically comes to a standstill, but after a few months what?s the hold up? Generally babes start sleeping through the night at 6 months, so you would assume that by 6 months (generally) everyone is well-rested. Is it just an age thing?
I don?t expect you to tell me the intimate details of your relationships, which is of course sacred, but I am genuinely curious what the reasons could be and thought hey! Let?s ask the internet! Maybe you all could either shed a light on the matter, or even just hypothesize with me.
And I seriously don’t have ANY pictures in my folders that I could associate with this post