As the 'pop' generation of the 1960's grow up and pass along, a new generation arrives, who'se expectations are very different.
Tribute bands - unheard of twenty years ago are now a staple part of modern entertainment. Likewise 'reality' TV 'talent' shows are hugely popular.
A pop fan from the 80's is now a mum of two / three who likes a night out reliving her youth - an instant concert audience for bands of the day.
The problem is - as John Lennon memorably pointed out when asked about re-forming The Beatles - "It wouldn't be The Beatles, it would be four old guys who used to be The Beatles."
That essentially sums up the 're-form' culture - but because the majority of audiences for this type of concert are not that bothered about the level of performance or the validity of re-cycling hits from twenty-plus years ago, there will always be money to be made, and that is, and always has and will be, the driving force in popular entertainment.
As a passionate music fan, I prefer bands who have simply aged - as we all do - rather than retiring and then coming back to pretend they are hip and trendy.
Stones - fine.
NKOTB - nooooooooooooooooo!!!!!!!!!!!!