A discussion about ethics must involve a discussion about the effects of a system of ethics on a group of people: This is a real-world effect that must have it's issues and priors spoken about, or you risk creating an ethical system for a group of people that will inevitably destroy them (which I would argue is bad, but I guess that is also debatable).
Such a discussion is about something tangible, and not purely about held opinion (i.e. you can go out and test it). I can see how someone might find that engaging. You are right that I usually do not (unless my conversational buddies have something novel to say about the subject, I find it extremely tedious). It is a good point, thank you.