"I open up to you, why wouldn't you open up to me?"

Maybe because it isn't safe.

Liberals open up to me about their politics all the time. I know them well enough to know that with most of them, opening up to them about my politics is not only not welcome, it can be dangerous. They find themselves confronted with an idea they don't like, and they will either quietly hate you forever, or, more likely, tear into the opposition with all sorts of "shut up and get out" trump cards. You're a racist, you voted for HIM?, you're selfish, you aren't a good Christian, you only want what's good for you and you hate everyone who needs help, and the list of trump statements goes on and on and on.

It's the same with emotional opening up. You may threaten someone with your statements and their first resort is steamrolling, name-calling, absolutism, poisoning the well, withdrawal, or even abandonment. All my life I've met people who deal with their families and friends with these bad techniques. People don't feel comfortable opening up to them. It's safest to hold your tongue. The exceptional person is someone like you, who can filter out these trump-card bulldozer statements and actually but in and hold a conversation with them. The rest of us don't deal well with this kind of bullying and we avoid these people.