When you think of it you might realize that most music artists have their chart success when they are between 20 and may be 35 years old. That makes averagely five to ten years. Take Pink Floyd or The Rolling Stones for example. They were all over the charts in the 1960s and 1970s with Pink Floyd's The Wall being the last album in 1979 to score a single as hit.. The Rolling Stones kind of fizzled out in the late 1970s while Mick Jagger had a few singles in the 1980s as solo artist.
My favorite pop stars from the 1980s when I was a teen and twen are Howard Jones and Nik Kershaw. From what I read is that Nik was pressed onto the bubble gum pop track by the music label but had huge hits on his 1984 albums Human Racing and The Riddle, scoring several hits from each. Besides one or two singles from the following album that was it for him. Not bound to the label anymore he continued to produce rock albums but never had any chart success. He and most other "80s stars" are still on tour and play their charts hits from the 1980s for their ageing fans.
There are a few exceptions like Madonna. Starting 1982 she had a string of hits until today. But I doubt that for example Miley Cyrus, Rihanna or Beyoncé can follow Madonna's footsteps to keep being successful.
Why is that? I can only assume that most of the music artists are not able to adapt their music style to please the young generation. Seems only Madonna and a hand full of other music artists.