What went wrong?
Drugs. When your main songwriter decides to retire to bed your music isn't going to be the same.
Also the quality of the music didn't go down until after 1973. No point in listening to much after 1977. After Endless Summer they became an oldies touring band.
THEY
FUCKED
WITH
THE
FORMULA
HEY
NOW
WELL
IT'S
A
Brian didn't put out Smile on time. It all went south from there.