Part of this is due to our being participants in what a lot of people, rightly or wrongly, regard as a somewhat exotic or even odd sport. We have that strangeness in common, if nothing else.
On a more serious note -- a large part of what most of us are doing is based on a desire to connect with the history associated with the type of guns we shoot. Not to say that everyone gets involved in reenactment or trekking or what-have-you, but the idea of Daniel Boone, Jim Bridger, David Crockett, etc is generally somewhere in the backs of our minds when we take our longrifles or Hawkens (however historically incorrect in the eyes of the purists -- sorry, couldn't resist a little jab there) out to the range, the rendezvous, or the woods. And, through even casual acquaintance with the historical times and people our guns connect us to, we can't help but pick up on the idea that, once upon a time, you offered help when it was called for. The offer might well be refused, but you offered. It's a trait that to a large degree is missing in our society today, this willingness to offer help and lend a hand ("ain't my job -- ain't my problem -- don't get paid to do that -- don't want to get involved -- just plain don't care...."), and to some extent a lot of us are acting on a more-or-less conscious decision to be a little more like people used to be, and a little better than the world around us. Plus, and probably more important, we're doing this to have fun, and for most of us fun involves including other people.
I like the black powder shooters I associate with precisely because they quite often talk instead of shoot. I grew up in an environment where, when you were at the range, talking was a strictly controlled activity, to be carried on away from and either before or after the business of the day, which was SHOOTING. Intensely, fanatically, spotting-scope-and-calipers-to-measure-groups-always-at-hand, do-not-bother-me, SHOOTING. Yeah, in case you were wondering, it was a kick in the butt for a kid. My dad avoided those people in both his shooting and fishing circles (and actually lost a few friends) once it became obvious that this was serious business and his kids weren't welcome. For that I've always been grateful, and to this day I'm just as happy to be talking -- and helping -- particularly if there are kids involved -- as I am to actually be shooting.