The difference is that OuTW wasn't a big hit in the US. It made about 1 mio $ (which is not too bad for a foreign film), compared to the 6,11 mio $ for GBU (FoD 4,25 FFDM 4,34).
(All peanuts compared to US hits like Butch Cassidy 45 mio or Little Big Man 15 mio or True Grit 14 mio)
But in Germany it became one of the biggest cult hits of all times. Even in smaller towns you will still have no problem to see OuTW on the big screen (I have seen it in cinemas alone about a dozen times (uncut of course), but, sob, I have never seen one of the dollar films on something bigger than a TV screen).
Also the music of OuTW is here more popular than any other Morricone work.