You question whether it's really seen as that eccentric: I've actually corresponded with a bunch of UK philosophers about Wittgenstein, all of whom regard his earlier work as vaguely interesting if subsequently outmoded (a more or less accurate assessment) and his later work as eccentric and mostly irrelevant to serious philosophy (a totally wrong-headed assessment). I'm happy to send you email extracts if you still doubt that.
I should note that I studied philosophy here in the UK (at Oxford), so perhaps I'm biased towards the UK. But I think this applies to the US too: Wittgenstein sort-of influenced the American tradition via Rorty and Kripke, but he's still not central to modern American academic philosophy. Kripke got him totally wrong anyway, and Wittgenstein's only a piece of Rorty's outlook.
As to your last comment - what you seem to be saying is that this is highly improbable based on 'well if it's that good why doesn't everyone believe that' considerations. To which I'd respond: (a) it's not a totally obscure work. In fact, it's regarded as the main late Wittgenstein work. But (b) late Wittgenstein is totally undervalued by the mainstream of academic philosophy, mostly because (I think) he renders it irrelevant; and (c) you're better off actually reading the thing and deciding for yourself. Otherwise you become a sort of 'efficient market theorist' w.r.t. academia/books. Not a position I'd want to hold, personally.