The question has many points of view.
Here is one
When the teams are not very big.
There is a desire to create more teams.
This leads to more interesting competition between the teams
Yes, at first this game was created for battles between associations. But many players show by their actions that they like more when friendship win, not winner of wars. And you saw vivid example of this in world Masters last year. And very maybe similar will happen in world Festival soon.