I think many people with a talent gradually lose the creative spark as they get older (not totally, and not all, but many do).
Cole Porter wrote some great songs/musicals when young & middle aged but could not write such great songs later (the musical Kiss Me Kate was a "hit" in later life after many years in the wilderness).
Issac Newton came up with some amazing ideas when he was fairly young and then struggled in later life to match them, as did Albert Einstein.
I guess those with talent have a certain amount to "say" and then once that has run out it is hard to find more to say.
I was listening to some old Beatles songs the other day and when I heard Eleanor Rigby I thought I bet Paul McCartney listens to that and thinks "why cant I do that any more".
Of course styles change as well, and a "hit" song in the 1960s or 1970s may not be a hit song 40 years later.