I think that experienced/skilled dancers have reached their main goals and have kind of build a social platform in the community. They can be more relaxed and invite more freely. In other words, they can be more open/ generous than before.
Yes, but also generous dancers tend to get good, because it's more of a challenge to be generous. If I only dance with a few leads who will lead familiar sequences, I might never look bad or feel frustrated, but I won't improve. If I dance with a beginner or a newcomer or even just someone with whom I'm not very sympatico, that's a challenge and I can learn from it.
When I say selfish, I don't mean selective or self-aware. Selfish dancers (in my experience, which is pretty extensive) only and exclusively fixate on what makes them look good or feels good to them; for them, a dance isn't something we're enjoying together. I've danced with many leads who were sure they were leading something that they were, in fact, not leading at all, but they'd gotten used to dancing only with familiar partners (even the most insecure will sometimes ask an unknown quantity to dance if she has spectacular boleos). They get frustrated and they complain,* because they see our dance as something they're getting from me (and they're not getting from me what another dancer is), not as a something which we are sharing. In a milonga, I just won't dance with them again. In a class, I'll ask the instructor for help: almost inevitably, the instructor will assume that I'm doing whatever it is wrong, because the lead has done this "correctly" with other follows, they'll dance with me, step back and say "that was perfect," and spend 10 minutes working with the lead who, it turns out, doesn't actually know what he is doing after all. Had these leads been in the habit of being more generous all the way around (approaching the dance as a shared enterprise, dancing with an unfamiliar follow now and again, etc.), they might have learned how to do whatever it was correctly in the first place, just as a follow who was more generous might have figured out that they were back-leading instead of following.
* If you have to tell me that you're leading something, my friend, you are not leading it.