Basically: in 1.0 people complained about relying on other people in an MMO (the horror, right?) so now the majority of this game is solo based, forcibly. In 1.0 you had bits that were solo but you had forced 2-7 minimum (+you) so there's no real reasoning, only thing SE has said in regards to forced solo: People will want to team up to overpower stuff like quests and so on. This was said during beta iirc since yeah it was brought up around P2 and 3.