Good observation. They say correlation is not causation, and maybe they're right. But I believe you can find a lot of evidence with correlation. For instance Paul McCartney's (a huge dope champion) production after the sixties was mostly garbage. He wasn't the only big name, dope-smoking rock and roller who did all their best work early, and then produced crap later. Is there a correlation between heavy dope use and dulling of the creative senses? Maybe.
Heart of the Country - 1971
Band on The Run - 1973
Jet - 1973
Live and Let Die - 1973
My Love - 1973
Listen to What the Man Said - 1975
Silly Love Songs - 1976
Let 'Em In - 1976
Mull of Kintyre - 1977
London Town - 1978
Girlfriend - 1978
With a Little Luck - 1978
Rockestra Theme - 1978
Goodnight Tonight - 1979
Daytime Nighttime Suffering - 1979
Wonderful Christmastime 1979
Coming Up - 1980
Ebony and Ivory - 1982
Take it Away - 1982
Pipes of Peace - 1983
No More Lonely Nights 1984
C'Mon People - 1993
Hope of Deliverance - 1993
Freedom - 2001
Ever Present Past - 2007
Or it could be that people get older and escape the passion of their youth.
But whatever the case, at the age of seventy one, Sir Paul McCartney (net worth 1.1 billion dollars) can fill any arena, auditorium or stadium in the World.
He is currently on his "Out There! Tour" and your comment makes me suspect that you may be the person on drugs.