What's the alternative? Do you really envisage a blockade on books crossing state lines? What's next, Smokey and the Librarian?

To put it less confrontationally - the books are banned from schools and public libraries. They're not banned from private purchase or private ownership. You can give these books, you can gift them, you can sell them, you can loan them. Just not anywhere that's publicly funded.

So there's really no difference between them being available from Brooklyn Library and being available from Amazon. As long as Texas isn't funding the BPL, there's no issue here.