Some of the responses sound much more like extended unstructured internships and work experience, rather than volunteering in the broader sense.
Perhaps there’s a different emphasis towards individual contribution in the US because of the emphasis on individuality but elsewhere there is a strong societal expectation that if you want to be part of a community and gain by its benefits you should also invest in its social capital, much of which involves volunteering of one sort or another, eg Meals on Wheels, coaching kids football, mentoring or whatever.
Not everyone can volunteer, but often its put you in positions of responsibility and leadership way ahead of your academic progression, and gives real insight into your abilities to balance serving yourself versus community, and what you’re likely to be as a grown-up [and at 20 you’d are most definitely not be yet].
People I’ve recruited who volunteer almost always are more mature, flexible and empathic. They often say time spent volunteering recharges them, because they gain so much back from experience.
In some cultures lots of that isn’t even called volunteering, it’s what you do in your own time. Some of it would be considered a hobby (coaching), some would be a favor you do for a neighbor (mentoring, tutoring or babysitting). I’d never thought of “teaching Sunday school” or “helping someone with their Chemistry” as “volunteering” until I had to fill up a list of “volunteering stuff I’ve done” for an American employer. The US has a heavy focus on marketing everything, on making everything you do or have ever done have a business use.
I have to admit I’ve been surprised at what a big deal volunteering has become as well. My nephew was recently accepted to the University of Oregon with pretty mediocre grades and test scores. But the standout thing on his application they even mentioned during orientation? Volunteering! My parents run a major medical mission to third world countries that treat hernias, breast cancer, dental issues, and provides free prosthetics to hand amputees. As such, my nephew has gone on these missions and has been a tremendous help to the doctors, nurses, and dentists, who all wrote wonderful letters of recommendation for him. He was especially complemented for his ability to reverse engineer equipment as a high school student, bringing a mammogram machine back to life that had been dead for over a year in a jungle hospital in Ecuador that everyone assumed was ready for the trash heap.