No shade, but Britney really hasn't been a 'main' popgirl since 2008 / Circus era.
Even if you look at Femme Fatale, her peers were still outselling her (in both singles and albums) by a fair margin

(although it was a big success for her in her own right)
She is lucky to have such a loyal fanbase that still keeps her on the charts these past few years, i mean how many other acts from her debut can still chart solidly without much support radio? (not including Bey and Justin because the GP is still here for them)
Basically what im saying is her major commercial days have been over for some time, her fans should be happy that she made a great album nearly 20 years into her career.