I have very early memories of library volunteering. My mother used to do deliveries of books to housebound readers, and in the school holidays, we used to go with her, and Mum's ladies used to give us a sweet or 50p while we helped put the books in and out of the crate, and they complained about a book being too racy (or in one or two cases, not being racy enough!) I wonder if services like that still go on - because it was also about social contact, not just reading. And it meant I learnt that warden-controlled flats existed.
There was also the provision of large print books, books on tape (before such things were commonly available,) sets of plays and music for local am dram and musical groups. There was so much more than just books.
It was also my first Saturday job, and I worked in academic libraries for a couple of years, until I realised than even getting qualified was likely to leave me in poverty forever. And that's partly the problem, that many people who work in libraries love it, so put up with the low wages, and people volunteer for the same reason.
(Couldn't afford to be in the union when I worked in libraries, but have paid my dues ever since.)