I actually think this is quite normal and is more of an insecurity thing. There are people who I've seen for years in my scene yet never say hello to. I'm sure they think I'm a snob or something. But in reality, i'm just really shy and after a certain amount of time has gone by without introduction, I feel kind of awkward going up to them, yet if they came up to me, I'd greet them warmly. In these situations, whose responsibility is it to break the ice? I think most people in the salsa scene are quite shy and introverted, but it comes across as aloof, snobbish, elitist, etc.
I've had a few instances where I've had wonderful dances with a follow, but the next time out, they act as if they don't even know me. Maybe it's because I didn't pay them enough compliments or didn't ask them for a repeat dance, so they figured I didn't like the dance. Or maybe they are just as shy as I am. We think that the salsa scene is different and that everybody should be nice to us, but people still carry their prejudices and social awkwardness with them into the scene.