I really hope this question wasn't prompted by dudes always sniffing your hair, because if so I'm going to be involuntarily shuddering all week, and my advice is to carry a stun baton around and MY GOD HE'S RIGHT BEHIND YOU!
But I'll protect my own sanity by assuming you've seen this a lot in movies and on TV and that's why you asked. And yeah, movie dudes seem to love the smell of hair, that's true. I think it's more of an old screenwriter's trick to show "he's into that girl." Sort of like how to show someone's depressed in a movie, they always pan to an old framed photo of a boot. We know that's not realistic, but we all "get it."
Don't get me wrong; chick hair smells fantastic most of the time. And there's no question men like the smelly oils you've got all up in there. But I doubt most guys would actually go for a hair sniff if they weren't already in bed with you, married to you, or had some other equally believable cover story.
So the short answer is: because it smells good. The long answer is that guys don't really do that very often in real life, unless I've been attending the wrong orgies.
I've had men do this to me on more than one occasion. I don't think it's as rare as you think. However, each time I was either on a date or with a romantic partner so there was nothing bothersome about it. And really, I take pride in my hair- so I simply see it as a compliment.
Why do we hold hands, kiss, caress, or hear our partner's voice and smile? It's a personal thing, we all have different things we like (touch, smell, sight, sound). Smell is most connected with memory. I'm sure you've noticed how if you smell something it evokes memories and feelings (good or bad).
My ex used to always smell my hair, even before we started dating. He was discrete about it at first, but then it was an obvious running joke with us. I dated one guy who would quietly inhale me. It's all apart of taking in the person you're with. If it's desired affection just enjoy it.
Personally I'm more about sounds so it's much less obvious when I'm taking in a moment. I remember tone, breathing, words and enjoy replaying conversations or moments in my head all the time.
Maybe I should get a stun gun or something, because I'm always catching guys leaning in to "take a whiff," like they're amazed I can smell good and not be a bitch-vixen with a whip and high heels.
Their eyes roll back a little, and they drawl, "God, you smell gooood..."
I'm always like, "Uh, thanks?"
It's more than a little unsettling.
Supposedly, that's where most of a female's pheromones come from. So, yeah.
What a lovely day for a 3941135! SCK was here
What a lovely day for a 3574323! SCK was here
What a lovely day for a 936505! SCK was here