A library can choose what books they stock (especially a school library. Of course they're highly curated.). You don't have to agree with their choices, but the book isn't banned. You can still find it at a county library, an ebook library, or on the Internet.
So it's a bit dramatic to say "I'm fighting the system by hosting banned books!", just because some Tennessee elementary schoolers can't check it out from their school library. Just feels like a joke and a mockery when there's governments that genuinely censor books.
Once the books go out of copyright they will no longer be able to legally prevent anyone else from printing the books, and copyright law doesn't prevent people from legally reselling their already-purchased copies of books. But if you go onto Amazon right now and look at prices, you'll find that a copy of one of the Dr. Seuss books that the rights-holder refuses to print more copies of, such as McElligot's Pool, costs over 100 dollars; whereas a Dr. Seuss book that the rights-holders haven't judged as racist, such as The Cat in the Hat, costs about $5.
Edit: per the other comment's Wikipedia link, the unredacted Operation Dark Heart seems banned in the US because it included classified info
Although copyright-infringing books may be illegal to redistribute in general, the difficulty in determining what counts as copyright infringement and what counts as fair use means you can't really tell for sure which books are illegal to distribute and which aren't, so I'm not sure that really counts as "banned". 60 Years Later had an actual court order which makes things a little more concrete.