Expert: Mike Caldwell - 9/12/2006

Question
why was there only 5 seasons when they were so hot in that era of time.

Answer
Believe it or not, they never made the top 25 during the original run of the show (through the final season, ending in 1974).  The Brady kids had a wild adolescent following, via fan clubs, singing tours, and the like - BUT in terms of pure ratings, they still never were high up in the list!  

Cancellation came at the hasty decision of network executives, knowing that they were fed up with Robert Reed's complaints and tirades.  Reed was to be fired, that was a definite, and they were stuck for a solution as to how to continue the series.  Some of this is detailed excellently in another experts posting by Mark Daniels at
http://experts.about.com/q/Brady-Bunch-1365/Robert-Reed.htm

Finally they just decided to cancel it altogether, since it was never a top show in the ratings, and I had read that the newly emerging "Sanford and Son" was making a massive dent in viewership as well.  Once syndication kicked in a year later, the popularity of the show really began its gradual, but steady, increase.  By the 1980s, syndication of the show was so rampant, many localities could see as many as 3 episodes a day!  Such repetitive airings really started to burn into the popular culture, and the massively popular show as we know it today was truly a product of, well, reruns.  

It's amazing the show was cancelled so hastily, but it may have been better than running another 5 seasons and turning the show into another "Jump the Shark" story...

Thanks for the interesting question
Mike Caldwell