I dunno about the metric you are judging volunteering on here. Do the people who don't volunteer and don't work have enough money to get to the place where they will provide the volunteering service.

As context and a little thought experiment:

I have just switched careers and have had to cut back on expenses to a bare minimum while I was learning the skills required to get a job in my desired field. I had decided not to work and focus 100% on learning. During this time I barely left the house and if I did I would walk, sometimes up to 10km, because I didn't have the money for even the train (food and rent come first). On the flip side my mother was a housewife while my dad worked (very traditional I know!) but she would volunteer in 3 different places because she could afford to (time and money).