As to why it exists, the answer is the same for just about every other linguistic feature: nobody really knows.
Positive on the Z. Fight me.
In all seriousness though, nothing drives me more nuts than asking questions you don't actually want the answer to, or are just asking to fill the silence. It's gotten to the point I ask people if they are really interested in the answer, or are they just looking for small talk,
Generally, I'm happy to talk with people, but I am not a big "small talker", because I'm generally a "communicate to problem solve, otherwise do" type of person. Building a relationship with someone requires over time I consciously build and try to track conversational contexts to facilitate faster, more efficient communication.
The process of doing that requires a significant investment of time not just to speaking, but to listening, building and working through conjectures, and familiarizing myself with how they approach problems, and determining how differently they do so from me
All this information rides along in my head all the time. The friendships and working relationships you build through such a process are unmatched. However, it takes significant effort, and it can lead to some awkwardness when you start actually noticing where the rougher edges are on who you're talking to.
I'm not one to leave a rough edge unsmoothed, but committing to help someone smooth out a part of their character in a way you can actually productively help is also a non-trivial task.
Some level of all of what I've described goes on in every encounter.
This makes people who ask questions they're not really looking for a true and substantive answer to incredibly annoying. It paints the picture of a person using me as a means to soothe their own discomfort with doing whatever they need to do. It's...trying on the patience.