I never practiced "idle conversation with a complete stranger" like that because I was lazy. But I did practice making normal, non-sexual, conversation with women on dating sites and dates so that I could go from "isolated in school, then after going online, low response rate and never more than 1 or 2 dates" to someone in a long-term relationship. And recognizing that sort of "ok there's just not any interest here, move along" signal was definitely relevant there too.
Skills take investment.
My parents didn't give me nearly as many opportunities to practice these skills as they had when they grew up, and pop culture actively encouraged me not to talk to strangers as a kid, so I had to work harder at them as an adult. But it was worth it.
It doesn't. It just helps the speaker.
Once you have shown that you are interested in someone by listening to them and thereby learning about them, you might sometimes find that they might also be interested in something you can share with them. The easiest way to get someone interested in you is to first get interested in them.
It's a pretty simple principle, but since people like to talk about themselves they often do not follow it.