The people who would benefit from the advice (resourceful people full of free time that are doing nothing meaningful) will likely ignore it anyway.
Can you go to a poor area and change it with a speech about ambition? Likely not that much. The issue there are not habits, it's an environment that disables dreaming big.
PG's text is for stragglers who were raised in environments that allow them to dream big, but they don't for some reason. That is such a low fraction of the world's potential, that seems like a waste of time.
Changing those environments I mentioned earlier is very hard. Absolutely brutal endeavour. I know hundreds of kids whose biggest dream is getting a high status paying job, because the entire environment shapes them for that. Those who can occasionally notice they can dream bigger ("doing great work") often feel intimidated, not uninspired. They can't afford to risk anything.
To me the greater change is possible on those environments who are intimidated, not the stragglers who feel uninspired.