^Well, many of these songs just work - because the audience loves it. Sure it might get bored to watch these songs again and again on every DVD but most of these songs just work live and the audience loves them. Of course Ayu wom't be like "Oh, the crowd loves evolution but I can't perform it - people don't want to have it on another DVD".
Still, it's not like it's only two different songs every year
Agree though about her having many great songs that didn't get performed yet.