Whitney's worldwide sales for I Look To You is officially 2 million now, and around 1 million shipments at 950k in actual sales. So it's not like age is a factor. Mariah and Whitney came out around the same time.

Memoirs isn't just a flop. It represents the end of Mariah the COMMERCIAL artist. She can no longer sell albums because she has alienated her old fans who used to buy her albums. Mariah is more like Rihanna now.