So I want to say I"m having the similar trouble with groups, but not exactly the same. I want to try to give you advice, but its just advice, not knowledge.

I feel similarly in groups. I feel alienated and I'm afraid to speak and get really nervous. But I don't go out of my way to greet people like you do. Try being aware of your tone of voice, eye contact, and body language. Are you being vibrant and open?

Some people don't engage others the way you do. They need to feel like you're excited to speak with them and they need to not be nervous. It's possible everyone you work with has troubles speaking, I can't be sure if I'm not there. Your workplace is not a great sample of people, it can be misleading.

I suggest that when your conversation dies you come up with something out of the blue that interests you. Keep it going, build momentum, but try to not feel unnatural. Do you feel unnatural when they answer and you don't answer back? Don't let that happen, then. Or if you do feel natural, accept the way things are.