By design, they are meant to be that way. I can only put emphasis on Chaman-Bourru's answer : Sometime you want to play with a good friend, and playing on regular mode is just boring as hell. You just steamroll everything without challenge. Epic mode are designed for these situation, they are not meant to be played solo. And if you don't want to play in group, that's not a problem since doing the different area in epic mode isn't required for anything, you aren't missing any content per se (Group quest and Group dungeon is another story, I'm just speaking about the regular playfield such as Thunder River, Ymir's Pass, or White Sand)