To be completely fair to those people, some of them do volunteer to righteous causes. But it's never enough for them.
The problem is that they're so heavily indoctrinated into thinking globally that local causes don't really do anything for them. In their mind, they don't see the worth in helping in a soup kitchen or running donation drives to help drug-addicted homeless people go clean, because it "only" helps their neighborhood or their city at most. Meanwhile, their idology talks about how the entire world is unfair and terrible and how the very fabric of society is woven out of the congealed blood of the oppressed and all that crap. At minimum, they have to "help" and entire demographic group, which is where you get the race advocates (read: racists).
Helping a single poor person or even a hundred feels like nothing to them, they can never be happy because their worldview is completely dystopic. Which is ironic, since they see everything through a lenses of class but refuse to look objectively at the most basic distinction of class out there: haves vs. have-nots.