The term “banned books” has become a pop culture meme. In this context it doesn’t literally mean banned, it means the book wasn’t allowed somewhere. In extreme cases a government in a controlling country may have forbidden the book.
However in a lot of cases the “banned books” were just not allowed in some school’s library for kids somewhere.
That’s why all of the books aren’t actually banned in the US and are readily available, unless maybe you’re a 3rd grader looking for them at some school library that probably wasn’t going to order the book for kids anyway before it became “banned”