I suspect that the combination of subgenres and the need to insure maximum ticket sales is contributing. I mean, seriously, how many metal fans will claim to be a fan of very band on the tour?
In my case, I do like every band, even if I don't own any Leaves Eyes. The whole chick metal thing hasn't worked for me in a long time. But they were cool opening for BG, and the other four bands are excellent for me.