Because there's one thing that's straight (and it's none of the male characters of the show) and that is that Marge has issues stemming from her mother's way of treating her. In pretty much every flashback of Marge's mother she has put down her daughter, or told her she had to be a certain way to be loved. This lives on in Marge insisting to always be perfect, non-confrontational and all smiles. Because if she isn't, then people may not like her.
But with Homer, she is secure enough to confront him, because she at some level knows that he loves her, even when he often takes her for granted.
What do you think? Hit the mark, or way off?