The clue is in the title "nostalgia tours".
That's why they sell well.
If Journey announced they'd play only Eclipse in it's entirety on their upcoming headline tour, and if the opening act was one of H.E.A.T, Eclipse, Lionville, Degreed, Crash Diet instead of Thunder and Whitesnake announced they were playing their two latest albums back to back.
It wouldn't sell fuck all.
The tours sell, because they are named acts playing greatest hits sets.
When I saw Styx/Foreigner and Journey a few years back, the place was packed, and after Foreigner's excellent hits-only set the girl in front of me turned to her mate and said "well they was quite good, but I can't believe after all that they didn't play "Just A Small Town Girl"..."
That's how it's seen and that's what people want. Greatest Hits bands that all just sound alike, upbeat pop-rock from the 80's with a few huge ballads thrown in.
Most people's dream tour on this site would probably be something Damn Yankees, a Giant Reunion and a Bad English reunion. But they'd struggle to sell out a small theatre (or a large pub!) in the UK with that line-up...
Niv