Why is it?

Why is it that most bands from the 70s, 80s, and 90s whom have had a catalog of hits go on tour now with new material but no one wants to hear the new stuff. It's pretty much like pulling teeth just getting through the new songs. I know why they do it. They have to. They have to promote their own album. Let's take Journey for instance. I saw them last fall and they every song they played was a radio hit at some point in time except for 3 songs from the new album that the crowd just growned through. Now on the other hand you bands like Metallica, AC/DC and U2 that put out new material and the crowd goes just crazy for it. Is it because they are still relevant? Is it because of the new generation picks up on these bands from Guitar Hero and Rock Band and that makes them cool? Or is it just a matter of taste? Or just some of those old bands just never evolved to the music of today. Some bands always say "well, on our next album, we're going back to their old sound", which they never do and why do it? Why not take a lesson from Metallica? They for example have never peaked. They always come out bigger and better with every ablum and it never sounds the same.