It seems like in ANY entertainment venue a new show has to be bigger and more extravagant than what went before it ...
great question chas, when DID it stop being about the music ?!? ...

I think 'Broadway' is about the only entertainment venue that hasn't changed all that much ... while there are still some grand productions, i.e. "The Lion King", most of 'Broadway' is still about the play: the characters, the plot, the words recited ...
And chas, why is it we don't see elaborate productions in Jazz ... I guess there it STILL is about the music - thankfully ...

t.