That's because of the love of books. I don't know how to describe it properly.
When I see a book I have read, it will take me back to the life I have read. Took me back to a journey that had nothing to do with the content of the book. I don't often think about the past, but reading old books can remind me of the past.
When I browse my library, it will remind me how my mental outlook has changed over the years. I used to be a naive child with an incredibly ignorant world view. Every book I read has changed my world view; Some of them happened in small ways, while others caused structural changes in my mental outlook. Every time I browse my bookshelf, I think of my personal growth. I have a poor memory. I can't remember most of the details of every book I read, but I can browse through each book and tell you how it changed my world view to some extent.
Books symbolize knowledge, understanding and wisdom in my heart. When I pick up a book, I can't see its printed paper. I have seen the thoughts, observations and wisdom of those who have experienced things that I have not experienced. When I picked up a book, I saw the perspective of the novel. Frankly speaking, it's exciting. I like that others have spent years developing their own ideas, and I only need a few hours or days to learn from them.
Some of us are just ordinary second-hand book collectors (no, not sex, you are so fucking rude: P). Books are just comfort, excitement and beauty.
I don't hoard my books. If a friend comes over and finds a book that interests him or her, I always share it with them with ecstasy. I even hope that they really read this book and want to discuss its contents with me.
I will never give away my books casually, because to be honest, the price of books is not the reason to stop those less fortunate people from reading (at least in the United States). Do people not study because they have too much work or something? My donation will not really benefit anyone, but it will be a great loss for me personally. If someone really wants to read a good book, all they have to do is borrow it from the local library for free! What concept!