People have no taste, especially American critics
+ she tends to bog herself down with filler (not as bad as pop girls with higher scores though, so that's irrelevant)
She should be higher, but it makes sense. It's hard to like her and get into her if you don't. Other pop stars can put out something good and you might not like them but you can get into that album/song. But Christina's style doesn't really do that.
I don't know if I'm making any sense here...
Because when people rate Lotus they say "Xtina should be recording better material like 21 etc" and then review Femme Fatale and say "Britney actually sang most of this record and some of the singles are kind of catchy" for example.
Because they are overloaded with filler/run on too long. B2B was her only good album and it would have been so much better if there wasn't a second disk
I love when haters bring this up. She has long albums yes but she actually has cohesive albums and the album tracks are integral to her story, Plus she takes much longer to release so those long albums are helpful to hold you over till the next one.
Not much else to it
especially when bionic and lotus exist 
