Speaking for myself, I’m too paranoid to buy a used book from some random charity because I can’t trust they ensure the books are clean before selling them.

My family brought home a bundle of music books from some charity event when I was a kid, and it unleashed an infestation of silverfish that proved impossible to get rid of. It’s been more than twenty years and they still pop up on my parent’s walls every few months.

Edit: to be clear, I’m not blaming the charities for this. Some people use donation bins as an excuse to offload literal biohazards - just ask a Goodwill volunteer how often they receive soiled clothing. Books are simply harder to check than many other goods due to the literal hundreds of hiding spots between the pages and in the bindings.