I watched a documentary in the late 90's (I believe it was called "the unreal story of professional wrestling,") that went into all of this. IIRC the shoot matches had no time limits and would degenerate into guys laying on each other for hours which hurt the appeal too.
In wrestling it isn't feasible to "lay on your opponent for hours" because once his shoulders are down, he's liable to be pinned. BJJ with no time limits does allow that, interestingly enough, since there is no threat of being pinned.
