It doesn't even translate in the book to be honest -- it undermines the power of the ring completely.Casual movie goers and non-book readers would have lost their shit wanting to know who the fuck the enigma of Bombadill was. The entire trilogy builds up this fear of the power of Sauron and the corrupting power of the Ring. You'd have the scene where Bombadill just puts the ring on and shrugs his shoulders as if it was just some trinket of junk completely unaffected by it. Zero explanation given whatsoever = doesn't translate well to film.
Tolkien also did this with Faramir and the ring, to an extent.