Most of this girls have new albums out, are touring or they are Taylor Swift, the biggest pop act this decade. Katy Perry is a great exception, I'm glad to see her there up there with no new material out.
You clearly are sure that there's not really a huge demand for Gaga's old songs right now, so why does it seem like you need validation?
You're right, maybe I shouldn't have included Beyoncé. She does have a 19 year career, while the nearest ones to her have 10 and 11 year careers.
Yup! Gaga becoming a legend in 1/3 of the time. Clearly in a league of her own. Katy, Beyonce, Rihanna and Taylor can celebrate those 200 combined sales somewhere else.
So I guess the answer is obvious.