Why is it that guys tend to open up to girls more than to their own gender?

Stigma. Men have been telling themselves to be a man since ancient times and many of them just can't open up to other men out of being laughed at, not taken seriously or judged. Also alot of men just don't know how to handle when someone opens up to them because they never got the experience with others or themselves.
It really sucks, I personally see a man who can be open about his emotions way more attractive, men who don't try to be men and just be a person whoever they truly are... Same goes for anyone I guess

They don’t want to feel or appear weak to other guys.

It's a male issue. Just like the ages old question "why don't guys ask for directions" when going somewhere.

Admittedly, over the years it has gotten better. Yet just last night a girl ask me for help in push starting their car. I don't believe the guy really liked her asking! Lol

Guys tend to want to fix things for themselves and if you give them enough time and space and encouragement they will usually be able to do that ,but there are sometimes they will reach out and it is usually either to another guy they trust and have known for a very long time or it is someone they are interested in romantically.
Usually, they are not going to spill their guts to their women friends, it's just the way many are .
I know that's not a popular thing to say, but it's what I found to be true and so instead of trying to talk them into something,I just let them be what they are.

Maybe they're afraid of other men seeing them as weak. A lot of the time, it's guys judging other guys for having feelings, lol

it’s a plot to get laid then they bust loose like OJ

Vulnerability isn't seen as masculine in a way, even though it's not true, it's just that idea has been prevalent through culture

I'd much rather consult with a lady myself.

for me its like that totally. I open up and tell girls things but its kind of I think because I feel more like a girl. But when it comes to like, HAVING sex... I am way more shy around girls but Im not really shy at all with a guy so idk why. everybody is different

Men don't feel the need to put up a facade of invulnerability around girls as much as they generally do around other guys.

I don't like opening up to women either. In my experience, women are even more judgmental and are likely to label you gay

I have found many women are easier to talk to because they are less judgemental and more accepting than most guys.

It's not easy to talk to guys with openness. Can't say what's the reason.

gender roles?

Machismo

I can't speak for anyone else, but for me, women tend to be nurturing, good listeners, great at sizing up situations, etc. They have a special energy that makes me feel comfortable around them. Got plenty of guy friends too, but women are excellent allies.

Competition and being perceived as weak.

Because males are assholes