Such a pertinent point! I wouldn't have nearly as much experience if I hadn't been lucky enough to get a paying job "in" (more like adjacent to, but in an organization who was super happy to let me work with the social worker on staff when I didn't have stuff to do in my actual role) the field. Plus I've stretched myself thin over my time in undergrad volunteering AND working part time for the past four years, and I'm sure at the very least my academics took a hit, but volunteering is important to me.
Especially with all this bullshit of the "unpaid internships" which is super aggravating. So I can only imagine the whole volunteer experience preferences lead to people who have been able to get those experiences because they haven't had to work as much while in school. It's a very annoying/frustrating conundrum!