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.
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.
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.
The majority of "banned books" are books that a random school district/religious school in a conservative part of the country elected not to include in their library at some point. Many of them are required reading in many other school districts and some of the most well known books of the 20th century.
The closer-to-banned ones are generally not included on banned-book-reading-lists and are banned on major retail platforms and long out of print and tend to be racist and/or genuinely subversive to liberal democratic principles. Most of these tend to be some of the most-downloaded-books-on-the-internet, and are also in no way illegal to own in the US - though possession of many is illegal in much of the EU.
An interesting case is United States vs Progressive inc [0] in which the US dropped a lawsuit to prevent a magazine from publishing a how-to guide on building an H bomb and Defense Distributed vs United States Department of State [1] in which the US federal government settled and allowed for the publishing of 3d printed gun files online, previously prevented under arms exports claims.
0: https://en.wikipedia.org/wiki/United_States_v._Progressive,_.... 1: https://en.wikipedia.org/wiki/Defense_Distributed_v._United_...