For Most of the old people collecting bottles, when they were young, China is very poor and have to work very hard to get enough food. I guess they are in the habit of hard working.
Do something and get some reward, even it is so small, is very different form do nothing.
In the article, "June" get a way to communicate with the neighborhood, and the people are kind to her. In this kind of mutual kindness, She feel her life.
I know at least one old timer (early eighties) that gets really happy when heading over to exchange his bag of aluminum cans. He lives in his daughters home and he doesn't really need money. My thinking is that it makes him happy to earn a bit of money completely on his own, at his age.
There's also a culture of no waste from that generation my friend's grandmother was more than wealthy but refused to eat with plates snacking with newspaper plates she made and grew a large crop of food in their front yard selling it to corner stores every year. She also would dig out clothing out of trash bins, wash and slice up the fabric to sew different clothes she also sold but didn't need to being fairly wealthy.