No woman knows because no man cares to explain.
I'm not sure that it's as simple as that. In my line of work I talk to a lot of couples and I find that men explain themselves quite well, women just don't like the answers.
I've found that women think men should improve themselves and become more like women want them to be. Men do it sometimes because holding on to a woman can depend on making those compromises, but that's not the norm.
Even this conversation, questions were asked, but then the answers were dismissed, and even though those answers were given in true TK sarcasm, they were essentially true answers. Women just don';t like it, and consider those kinds of answers to be some kind of moral defect. Only it's not a moral question at all, it's a biological one.
Men do like porn because of tits and ass. I mean that's not some deep dark mystery at all. They like it. I'd be more concerned with men if they didn't like it. Women don't like it, but I'd be worried about women if they all loved the tits and ass in male porn.
AND, there is nothing inherently wrong with men liking to watch women being fucked in every orifice they have and some only imagined holes.
Men don't share their feeling [generally] because they don't have a "need" to share them. It's not their biological imperative to sense need in other humans. That's a woman's biological imperative. We nurture. We need to intuit need. Men protect. They only have to be alert to environmental dangers. You don't have to be Einstein to see these differences.
What women need to do [in my opinion] is recognize the differences, work with what is there, and change some things if they can, but if a man refuses to be changed--don't call him an asshole for just being a man.
We've become so safe in our environment that we think that biological imperatives are passe. We're still animals. Born with certain instinctive imperatives. Sure they can be modified somewhat, but lets not pretend that men are all of a sudden not looking to plant their seed in every woman that passes by. That's what men are supposed to do. They in fact are driven to do it. Sure, many curtail that instinct, and bravo for those men and their self control and intelligence. But, the men who don't curtail those instincts aren't Neanderthals. They are just being men.
Why do men want sex when they feel strong emotions? Because that's how they express feelings--physically. Ever seen a man playing pool miss a championship shot? He hits the wall. Ever seen a man's mother called a whore? He hits the offender. Ever seen a man caught breaking into a home and trying to rape the females? He gets hung. Ever seen a man feeling love? He wants to penetrate a woman.
These aren't big mysteries. Men express themselves physically. Women express themselves emotionally and verbally. We do that among our respective genders because those are the biological roles we fill. men are supposed to protect and defend--they have to be physical to do that. Women raise the young. They have to be emotional and verbal to nurture and teach the young.
It's not calculus. And, of course there are exceptions. Not all men are alike, just as not all women are alike. But, these are basic true-isms that women just don't want to look at. I see women acknowledge it and say "sure, sure. Men are hunters, blah blah blah", and then still ask why men don't talk about their feelings.
To be honest, I consider it a weakness for women to need the constant "validation" of a man and his feelings. Men can be really interesting when they talk about what they want to talk about, but boring as hell when forced to talk about what a woman thinks a man should talk about.
It's just not a big mystery when it comes to men, and they are not some kind of lesser being because they don't act like women do, and if you all want a lover to go on and on about his feelings, date a woman.