AMOUR, I think, was too whispy and, as Brantley put it, "claustrophobically fey," to survive on Broadway. It didn't have much of an advance, and after the wildly mixed reviews, it didn't really have a chance.
It was also a show, like THE BAKER'S WIFE, that didn't have much of a plot to care about, and so had to resort to "local color" numbers (like The Painter's Song, the Whore's Song, etc.) that didn't seem to have much to do with anything.
The characters, despite the fairy-tale quality, were hardly developed at all, which resulted in them being either one-dimensional (Isabel's husband, the street merchants) or no-dimensional (Isabel, who really doesn't do anything other than love and be loved).
And, on top of all that, some of it was just plain weird. Isabel's Husband sings about his fantasy of being whipped (Every single time I'm beaten by a whore / I go to court and even up the score!). One of Dusolei's admirers, while he's in jail, visits and spreads her legs for him. Etc.
"Y'know, I think Bertolt Brecht was rolling in his grave."
-Nellie McKay on the 2006 Broadway production of The Threepenny Opera, in which she played Polly Peachum