...because it is fun to have an advanced rotation to play around with. the wonderful achievement it is....when you finally master it, that is gift that keeps on giving.
I'm all for a simple base to every spec don`t get me wrong, so a new or unskilled gamer could also enjoy the game. but there should also have been a vast system to build on this, so a player then could evolve..and skilled players also would actually have fun with the gameplay in wow.
this is not the case now. the only aspect interesting in legion pve are boss mechanics. most classes are completely uninteresting to so many. and that is not particularly clever by blizz in game where building your toon is one of the key attractions. wows gameplay are a borefest