Because she tied the record with Michael Jackson .In music history , only Katy and Michael achieved this.
Once again, this does not make her the female MJ.. It took ALOT for him to get him all he's done.. Katy has yet to even do HALF of what he's done.. Just saying..
They were pressed, considering they even give Rihanna credit for 3 #1s from Good Girl Gone Bad when two of those three (Take a Bow and Disturbia) were on her re-release, but the chart positions Billboard published themselves don't lie:
#1 - California Gurls
#1 - Teenage Dream
#1 - Firework
#1 - E.T.
#1 - Last Friday Night
#1 - Part of Me