Because players want consistent and smooth runs in the groups that they create. If you did raids, you’d understand where this is coming from. There are some mechanics where a single player can cause the raid to fail. So it is in WoW. I killed few bosses in GW2, and for most part is targrt dummy simulator with some short fazes of activity. It’s not as dumbed down as you make it for those that are not experienced enough at the bosses. This is evident if you ever pug them or try to bring in pugs to your statics. Well yeah, different teams approaches bosses differently so new player in team may need 2-3 wipes to see how you do it. I don't see a problen here though. But I maybe GW2 people are too used to one shotting everything, and because of that they concider a wipe as natural disaster.