Comment by wiml

This is only really true for books published during a certain interval when high acid (wood pulp) paper was common. Before the late 1800s paper was typically made of other plant fibers ("rag"); by the mid-late 1900s de-acidified wood pulp paper was cheap enough to be common. Many books today still have a small remark in the front matter telling you that it was printed on low-acid paper and will last.

Pulp paper was much cheaper, which is how lurid mass-entertainment paperbacks came to (a) exist at all and (b) be called "pulp fiction".