Speaking for myself, I'd say it's one or more of a couple of things:
1. I find something that I find interesting, and speculate that perhaps other people would find it interesting as well. So I share it here in the hopes that somebody else will enjoy it. There's no expectation at all of getting anything "back" from this interaction other than a subject sense of self-satisfaction for doing something I consider cool.
2. I find something I find interesting, and hope that maybe a fascinating discussion will be sparked by sharing the link here, from which I may learn interesting new things I did not know. A good HN conversation is one of the most wonderful things on the Internet, IMO.
3. I have some "thing" I want to promote - something related to my business, or maybe a philosophical or ideological position I want to advocate for. I may share something here that promotes that agenda in some way.
Out of those three, number (3) is by far the least common. I rarely post anything that's blatantly self-promotional (even though it is allowed here, as long as it's not to excess) and don't post extremely ideologically slanted things terribly often. Most of mine fall into (1) and/or (2) for sure.
but beyond that does it really translate into commerce and connections for people ?
Occasionally yes, in my experience. But I personally consider that about the least important reason to use HN. YMMV. shrug