Because the Salvation Army lives in the late 90's-early 2000's when their fave was the top girl and can't accept the fact she has been forgotten by everyone but her fans, who aren't even buying her music.
To compare their "peaks" is stupid because 1.) Britney was THE girl back then and was releasing when Pop was very popular during the time people bought albums. 2.) Beyoncé was part of a group while Britney was accomplishing this, but the Salvation Army complains when you use the group's receipts to compare to Britney, 3.) Britney has decreased in sales since Beyoncé's solo debut, and the Salvation Army are STILL pressedT at the fact someone their fave was once outselling has been outselling their fave for 11 years.
Beyoncé's legacy, longevity, and impact are completely ignored and denied when Beyoncé has influenced more of the girls today, including Britney. Oh well though, I'd be upset if my fave went from selling 30,000,000 albums to less than 700,000.