Why Are Bosses Of Some Quests 30 Lvls Above The Quest?

Why do you label a quest at a certain lvl but the bosses are 10, 20 and sometimes 30 lvls above the start of the quest? Why not label it higher and save some of us the frustration?

 

with a couple exceptions, bosses are designed to be beaten at the level you unlock their quest. their level does not indicate the level you need to be to beat them

 

Bosses are usually labeled much higher in level than what level you probably are when you are fighting. This doesn't change a lot of things, I usually don't even look at the levels of the bosses because they just don't mean much.