Because they've got great, catty fights.
One of the first episodes I watched had a fight with them. It was back when Tea was Matt's lawyer. All I remember from the fight was a line that went something like this.
"I found you whore-izontal!"
I can't remember if it was Blair or Tea, but I thought it was hilarious.
"I want a lap dance from an octopus."
-JG2