More than 10 years ago, when these pop stars released either a single or an album, their material could easily go straight to number 1. They were often invited to close or open awards shows, and fans lined up to buy their music (that is, back when CDs were popular).
Today, it looks like fans have forgotten about their music. Or perhaps their star has dimmed. Or perhaps the music industry has changed (i.e., downloadable files vs physical copies).
Whatever the reason is, the numbers don't lie. These pop stars aren't as "best-selling" as they were a decade ago. In fact, their latest album flopped. Take a look.