As someone on the other end of this, I have my own reasons for mostly keeping to myself. I've been burned by sharing very innocent things at past jobs and have even lost one job due to it. I've had coworkers and supervisors butt into my private life.

In other cases - mainly with English teaching jobs - coworkers have said things that have made me extremely uncomfortable (for example - joking about violence at work, badmouthing students, talking about sexual topics, etc.), and as I didn't work with them directly anyway I kept my distance.

I'm not saying it's a great way to handle things, and I understand feeling kind of bad about it, but if you're on the receiving end of something like this just note it's not always meant to be an attack on you personally. Sometimes it's just a result of a bad overall work environment or experiences.