Answering the Rhetorical
Dear Rhetorical Question Answerer:
When did Motley Crue become classic rock?
Bowling for Soup
Dear Bowling for Soup,
Motley Crue began its transition from vital music makers to the classic rock and oldies market when they released
Decade of Decadence in 1991. Any time a musical group releases a greatest hits collection, it gambles. The very name greatest hits indicates that there will be no further hits as good, and a retrospective look at the band also makes the casual fan wonder if the band is done. Even if the album includes new material, its target audience is the cult fan who wants to own everything the band puts out and the people who, years later, decide they want to own a collection of the band's songs.
Looking over Motley Crue's discography, it proves true enough. Between
Dr. Feelgood and the two releases in 1994, two complete high school classes matriculated without new Crue, and you could only hear them on album rock stations and other retrospective-looking outlets.
So to answer your question, BfS, the best date we can give is 1991.