[techsupporter]

> nobody donates physical books anymore

It's partially number one but definitely this for me, insofar as thrift stores go. The two thrift stores around me that take books are Goodwill and the Salvation Army and I won't donate anything to them any more.

My book donations go to the neighborhood independent bookstore for them to price and resell and keep their employees paid.

The large chain bookstore near me still has several shelves of science fiction, new release and perennial favorites, so I think at least some are still being made and sold. Hopefully you can find what you seek.