I'm mostly just busting your chops...mostly. I do find it strange that because the subject matter doesnt have much to offer you, that you still couldnt find the film enjoyable. There are many great movies I can think of whose subject matters doesnt have much to offer me...in fact, just about ALL of the Coen Bros. are that way, but I can still enjoy, or even truly LOVE their films.
The Man Who Wasn't There, when I think about it as simply subject matter, is a pretty lame, weak, dull, etc. movie. It has almost zero to offer me, and I'm not a big fan of Billy Bob Thorton or Tony Shalhoub to boot. But damn it all if the Coen Bros. didn't turn out a damn fine piece of cinema with that one.
I just wanted to put that out there, you don't have to justify anything to me. Live and let live I suppose.