Britney has been a punchline for years now. Her bald head is her lasting memory, nothing more and nothing less. No one in the general public but stupid twinks with bad taste in music respect or remember her.
Britney flopping has been kind of overshadowed by gags her artpop era. She wont let her shine
Britney has been steadily declining since 2010 though.
Femme Fatale did well enough (just like how BTW was technically a successful era) but it was a clear and significant drop from Circus. And now BJ is just failing harder b/c she ruined her brand with XF + bad music (this is definitely the biggest factor).