I was pondering on this question recently when I was at the dentist. When I was shown in to the room the dental assistant asked the usual "how are you?" and I replied "I'm fine thank you," and the conversation terminated, as usual. But I was noticing that the similar introductory greetings that I could overhear in the nearby rooms went differently, with the patient typically responding with "I'm good, how are you?", or some similar reply, and then the conversation developed into a back and forth exchange that often would continue more or less indefinitely.
Even though I have learned, through observations like that, that one is expected to bounce the initial question back with a reciprocal enquiry about the other person, and that a conversation then develops, I just can't make myself do it. It feels to me to be so artificial and forced if one asks someone who is more or less a complete stranger, about how their life is going, and I simply cannot do it.
I was even prompted, after my recent experience, to ask a couple of very good NT friends of mine to guide me through an imagined encounter with a stranger, to teach me how to "play the part" of an NT in the exchange of greetings. We had good fun as they tried to teach me, but I think in the end we could all see that it was hopeless for me to try.
I think one thing that doesn't help, in my case, is that I am also very bad at recognising people. So in an instance like I was describing at the dentist, I'm really not sure whether the dental assistant who greets me is the same person who has been attending to me for the last few years, or if it is a new person that I've never met before. So I am never sure if I should be responding in the way I might if I had known the person casually for several years, or if I should be responding as if we were meeting for the first time. This ends up meaning that I tend to "overthink" the question, and I worry that anything I say in response might be inconsistent with one or other of the two possibilities. By the time I can work out a "neutral" reply that would be consistent with either having met them before or not having met them before, the opportunity for a spontaneous-sounding reply has long passed.
But even with people I know casually but I am sure that I really do know them, I still find it difficult to have a back and forth conversation.