I don't want to be pouring gasoline on the proverbial fire, but I am genuinely curious. J.R.R. Tolkien died in 1973, so even in the most permissive legislations his works will not become public domain until Jan 1, 2024. Or has Tolkien Estate specifically put The Hobbit into public domain?
Something to do with the vagaries of US copyright law? If it counts as a US-published work it might be treated as out-of-copyright within the US, even though first publication was in a different Berne Convention signatory. It's definitely still in copyright in the UK.