Britney's career is no different than Justin Bieber's.
The center of Teen Pop who spawned huge sales against competitors, and delivered an Earth-shattering hit, could dance their ass off, then went off the edge after a few years following constant ridicule (public thought she was a joke for the longest), and gradually declined by each era despite the huge star power.
Bieber will never be considered a legend if in addition he does an iconic VMA performance with a snake around him, and makes a few more hits in 5 years. The same applies to Britney.
People just feel sorry for her, honestly.
you're great too. 
