Originally Posted by
Rentahamster
Because it artificially boosts your stats based on an arbitrary number, and it rewards people for adding in afks, non-battle classes, and underranked people just to get the boost.
The only "party bonus" you should be getting is the "bonus" for actually putting together a good party that works together and reinforces each others' strengths. Each new member adds his own contribution because of his own personal worth, not because "oh we just need one more person, I don't care who, for the party bonus".