What were some of the factors that made people believe that rock and roll was dead by the early 1960's?

Rock N Roll appeared to have been tamed by the end of the 50's after the pioneers of the genre had all been hit by various scandals and tragedies.  Chuck Berry was arrested for having sex with a minor, Jerry Lee Lewis was also revealed to be married to his 13 year old cousin, Little Richard became a born again Christian and turned to Gospel Music.

There was also the tragic deaths of Buddy Holly and Eddie Cochrane in 1959 and 1960 respectively.

Probably the most famous case for the taming of Rock N Roll was the enlisting of Elvis Presley into the US Army and when he came out 1960 he was more interested in his Hollywood Career than his music.

I don't think people believe that. It's more like it died in the 1990s. 

Heck, the Beatle's were just getting started in the 60s.