The music career wasn't going well to begin with, right?
Her acting was always best when she did light things like "Monster in law" etc
Why did she have to go into more "serious" stuff? You won't be getting nominated for an Oscar anytime soon, dear.
And all that exposure of her relationship with Ben Affleck yawning by her side and being told off and stuff, just started making people dislike her (at least a little bit more justifiably than before, I'd say). So, it became more "acceptable" to write something negative about her, because she let various things slip from her side, the way I see it.