Let's see how they compare ever since Bey started her solo career cause this would be kinda the fairest way to compare:
Britney Spears:
'In The Zone' (2003) 8 million
'Greatest Hits: My Prerogative' (2004) 5 million
'B in the Mix: The Remixes' (2005) 0,5 million
'Blackout' (2007) 2,5 million
'Circus' (2008) 3,7 million
'The Singles Collection' (2009) 800.000 million
'Femme Fatale' (2011) 1,9 million
'B in the Mix: The Remixes Vol. 2' (2011) 0,1 million
'Britney Jean' (2013) 600.000
Total: 23,1 million
Norah Jones
'Feels Like Home' (2004) 12 million
'Not Too Late' (2007) 4.5 million
'The Fall' (2009) 2.5 million
'Little Broken Hearts'(2012) 1 million
Total:20.5 million
P!nk
'Try This' (2003) 3,5 million
'I'm Not Dead' (2006) 6,5 million
'Funhouse' (2008) 6,5 million
'Greatest Hits' (2010) 3,5 million
'The Truth About Love' (2012) 5,8 million
Total: 25,8 million
Taylor Swift
'Taylor Swift' (2006) 6,0 million
'Holiday Collection' (2007) 1,5 million
'Beautiful Eyes EP' (2008) 0,4 million
'Fearless' (2008) 9,5 million
'Speak Now' (2010) 6,0 million
'Speak Now Tour Live Album' (2011) 0,5 million
'Red' (2012) 6,5 million
'1989' (2014) 8,2 million
Total: 38,6 million
Christina Aguilera
'Back To Basics' (2006) 4,5 million
'Keeps Gettin' Better: A Decade Of Hits' (2008) 1,5 million
'Bionic' (2010) 850.000
'Burlesque Soundtrack' (2010) 1,4 million
'Lotus' (2012) 550.000
Total: 9,3 million
Shakira
'Fijación Oral, Vol.1' (2005) 4,0 million
'Oral Fixation Vol.2' (2005) 4,8 million
'She Wolf' (2009) 1,8 million
'Sale El Sol' (2010) 2,3 million
'Shakira' (2014) 0,9 million
Total:15.5 million
Alicia Keys
'The Diary Of Alicia Keys' (2003) 9 million
'Unplugged' (2005) 1,5 million
'As I Am' (2007) 6 million
'The Element of Freedom' (2009) 4 million
'Girl On Fire' (2012) 1,7 million
Total:22.2 million albums sold
Avril Lavigne
'Under My Skin' (2004) 9,5 million
'The Best Damn Thing' (2007) 6 million
'Goodbye Lullaby' (2011) 1,65 million
'Avril Lavigne' (2013) 700.000
Total: 17,95 million
and
Beyoncé
'Dangerously In Love' (2003) 10,0 million
'B'day' (2006) 6,5 million
'I Am... Sasha Fierce' (2008) 7,5 million
'4' (2011) 3,0 million
'Beyoncé' (2013) 3,8 million
Total:30.9 million albums sold
Conclusion: The only one who has higher album sales ever since Bey started her solo career is Taylor (and Adele). Now you know why shes considered the queen