The point of BI is that the government doesn't actually need to be involved in centrally planning all of the things that need doing— it's a huge amount of unnecessary bureaucracy when many of them are things people would love to do given freedom from having to immediately "earn a living".
So the government doesn't pay you to pick up trash in the ravine near your home. The government pays you because you are a citizen, and as a citizen of a wealthy nation, you deserve the basics of life. If you spend that life consuming fast food and internet porn, that's okay. But given the time and freedom to do so, some people will choose to clean up that ravine— they weren't directly paid, but having their living expenses covered made it possible.
Currently people who work volunteer more than people who don't work. Further more volunteers give only an average of 3 hours/week. That's not much, in the context of our discussion.
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).
I'm curious if such trash would ever be picked up. While I can imagine people being more altruistic once their needs are met, humanity seems to be really near sighted when it comes to subtle-yet-broad problems like trash. "Out of sight, out of mind."
So the government doesn't pay you to pick up trash in the ravine near your home. The government pays you because you are a citizen, and as a citizen of a wealthy nation, you deserve the basics of life. If you spend that life consuming fast food and internet porn, that's okay. But given the time and freedom to do so, some people will choose to clean up that ravine— they weren't directly paid, but having their living expenses covered made it possible.