This is the big thing with the Avril Lavigne debate, she so rarely tours, and literally never played festivals until this year. Its not just that she's an older act, or that people are "ironically" watching her as I've seen suggested, but that most people may have wanted to see her in the past but not got the chance.
Just looking at her Manchester gig history, she did Castlefield this year and Apollo last year (both of which were sold out very quickly and were hard to get tickets for nearer the time, we tried for Apollo last year), then before that it was 2011, 2008, 2004 and 2003. I've always liked her and wanted to see her, and now go to loads of gigs but wasn't financially able to go to as many gigs in 08 and 11, and was too young in 03 and 04, so this was my first chance to see her and I imagine a lot in my age bracket would have been the same.
Almost every other comparable act has appeared at festivals over the years, Glastonbury/Reading/V Fest when it was on/Kendal etc, but despite being around for over 20 years the opportunities to see her have not been plentiful.
Also, not one person we were with had even heard of Janelle Monae apart from me, never mind be willing to see her. and there was only ever one place I was going to be at that slot.