Why do rock bands have a limited period of creativity?

I agree with the dates you give for the bands you list. There are probably many reasons why bands have limited periods of creativity. One cause is that money begins to change everything for a band. When a band is young and starving, and everything is all about the music, then you tend to see great art being produced. When the discourse starts to turn into how many CDs are sold, how many arenas are sold out, and how much merchandise is sold, then that changes the dynamic bigtime. Another cause for the limited period of creativity is that as bands grow older, their interests widen. Their musical interests are now penciled in between family time, recreation time, promotional events, etc.