Why did Odile prefer Arthur?
Is it because he's the jerk who takes her for granted?
The classic "chick digs the bad boy" scenario?
Probably, which is part of why the movie doesn't quite work.
The problem with the film's logic is that Arthur is neither attractive enough nor successful enough for Odile to overlook the fact that he's a jerk for so long. Indeed, when women go for guys who look like that, we're usually looking for guys who make us feel safe in someway (which is why their having money or a caring personality often counts in an ugly guy's favour). Her preferring the "bad boy" just didn't work in this case because bad boys are typically a little younger (although I must say, Claude Brasseur makes for a really old-looking 28) and, well, handsome.