One difficulty is that many societies are very individualistic. People are isolated. It's not enough to say that your skills are valuable in the abstract. There needs to be work that's obviously worth doing, and this requires either demonstrated demand or a leap of faith.
This is fairly unlikely for someone who is depressed. Enthusiasm is very important and often in short supply.
Also, entitled customers will repel volunteer labor. Being paid is in part compensation for putting up with annoying strangers.
This is absolutely the case. It takes "second" (or more like 100th) order thinking to recognize that you're part of an ecosystem that will be less well if you stop contributing just because you're not being paid. The faith part is that you will continue to have your needs (not necessarily wants) met through reciprocity -- which is a basic human psychological trait, so not the worst gamble.
This is fairly unlikely for someone who is depressed. Enthusiasm is very important and often in short supply.
Also, entitled customers will repel volunteer labor. Being paid is in part compensation for putting up with annoying strangers.