It is the purest form of empathy and yet unfortunately also the most invisible kind.
Hell, I know people who tend to help themselves into dumb conversations while the other person reads a book or does something similar. No empathy here.
This is, I believe, to cover discomfort coming from silence and such conversations, while not completely pointless, often have little value. They would talk about just anything, to combat this feeling. Weather is a good topic because most people can relate and it is rarely annoying.
I would say that both intro- and extroverts can act like this but conversations started by introverts tend to be more awkward. I think that lonely people are more likely to start valuable conversations.
Sure, for their mental model of other people they're being nice (and in some cases they actually are) - but not everybody has the same mind or preferences. True empathy is built on understanding that.