Altruism is not a default position, and is unusual in the real world.
I'm not saying that's how it should be, or that people shouldn't work to make it otherwise. But you say why don't all those people walk away from that? How far would you go? What if you had children depending on you? It's very easy to condemn other people as "greedy" but you show a lack of understanding, of empathy, perhaps, for how people in general function in the world if you assume they should just do what you say because "obviously, my moral stance trumps their concerns."
Edit: I upvoted your other comment, by the way, where you lay out the very scenario I speak of. Many people are "screwed" because their lifestyle has expanded to their current circumstance. Few people realize that progress in some dimension rarely rules out regress back along the same path. Liberty requires maintenance, because there will always be societal forces aimed at eroding it.