From my experience you can’t devote 100% of your time to getting back on your feet and search for jobs. If you have trouble finding a job it gets too depressing after a while and you need something positive where you actually see results.

Volunteer work can come with benefits other than payment, such as food, access to facilities, etc. It can also provide a support network and contacts for finding work.

With that knowledge (despite not knowing specific circumstances), it sounds like a highly effective way to cope with the situation as an individual.

Why do most people have only one job? Wouldn't it be better to spend evenings at a second job and then have leisure when you retire?

I guess you're trying to make some point, but I don't really see it.

I think the point is that one can only devote a finite amount of time and energy searching for a job each day before they hit diminishing returns, due to both mental fatigue and physical limitations. Though as another commenter pointed out, volunteer work is a common resume-building and networking tactic.

The poster above you is making a comparison between working a job and finding a job.

Working a job: you spend 8-12 hours at the job and then spend your leisure time doing other things, like studying or meeting friends or watching tv.

Finding a job: you spend 8-12 hours trying to find a job, and then you spend your leisure time doing other things, like volunteering.

The question you posed earlier was, why wouldn't someone just spend all available time (let's say 16 hours per day) trying to find a job, instead of doing anything else, like volunteering. The poster above you was responding to that, trying to demonstrate how the same suggestion would be ridiculous in the context of working a job, and it should be equally ridiculous in the context of finding a job.

When I was unemployed in Boulder during the last recession, I wasn’t homeless but spent a lot of time in the library applying for jobs and browsing the internet around homeless people. I think volunteering helps people have a sense of community and keep sane during an isolating period.