I believe lots of player have 1-2 friends to play with. Its hard for them to join other’s party cuz they need to negotiate with party leader, ask permission to invite their friends in.
So most of these small group prefer open a new party to ask others to join.
That is why you can see hundreds of 5/8 6/8 7/8 in party list.
Why not make it easier for everybody to have this function to avoid wasting time on party build?