What do people expect in response to "you're very quiet"?

I've noticed this question/statement a lot here, especially at work. Sometimes by people who say no more than "morning" and don't attempt to make any further conversation.

Ive seen countless ways on how to reply to the question, but I'm more curious about the people who actually ask it, why? I always find it weird and it never really opens up any chance of a conversation anyway.