Reading skills here must be lacking severely.
After Katy none of the other popstars on Guinness made Forbes because they got cut off by R&B singers and rappers.
Hence the inclusion of them onto Guinness who basically just filled in the Forbes list
with only pop singers.
Beyonce, Jay Z, J.Lo, Eminem, Kanye are not considered pop singers by Guinness.
It's not rocket science.