Somethings do get passed on.
When we had to clear out the apartment of MiL, she had a sizable collection of books, and a bunch of clothes and shoes that had only been worn once. We tried the library and a few different charity shops, but for most things they said no. The books went in the trash and the clothes went in a clothing recycling bin - which I guess means they also ended up in the trash.
The physical book market is shrinking and a significant portion of new readers likely use ebooks/audiobooks instead so there's just far less demand for physical books.
I think it's going to be very hard to even give books away in the coming decades, I can see the vast majority going to recycling.
Book charities won't send to jails, only to prisons, because they say people aren't held long enough in jails, even though I know people who have been waiting 11 years for trial so far.
My local library will take books for their annual fundraising sale. But I suspect most end up recycled or tossed even so.
After the sale a large dumpster is parked out front and the volunteers fill it with things that didn't sell, to be sent off for disposal (recycling, I think.)
I wonder how it will end up, let the people pick interesting stuff and then leave some value there and have someone buy it in bulk or get all of it and save the cost to recycling and processing it.