Books are relatively inexpensive in the West. There are some exceptions, but this mostly remains true. Books are not as easily accessible in other parts of the world. For example, in Uganda books are incredibly difficult to come by. The cost is astronomical in a country with very low wages. Books there can cost a week’s salary, or more.
Which is why I’m saying don’t throw out those old books you no longer want. There are likely people in your area who simply can’t afford to buy their own. My top suggestion would be to take them to a company or organization that will do their best to reuse or recycle them.
But this applies to most things. Food. Clothing. Old electronics. So many things end up in landfills that could have been reused or recycled but simply aren’t. And I know some would say that books aren’t THAT important to go out of your way to preserve, but let me ask you something. Did you grow up with books in the house? Imagine if you hadn’t.