Well there isn't really a definite answer but what you're going through is not uncommon. Some may say that it's because some guys just don't like talking about their feelings and they don't want other people talking about their feelings. They're just for some reason really anti-feeling.
If things are going like this and you want to put an end to it, you need to confront him about it. Try being calm about it, but if he goes on being irrational and not giving you any good answers, then ditch that calm appearance and surprise him a little. Go ahead and get all crazy because I feel like your boyfriend kind of needs a reality check and a good verbal smack in the head. I mean seriously, what he's doing is seriously immature and just plain stupid.
And if worse comes to worse, break up with him. There is no point in saving a relationship where open communication is not possible. Open communication is needed in a healthy relationship. And if you can't get that out of this relationship, then just walk away from it.