The GNW system is horridly outdated and insufficient, there's nothing you can do about how group behave in GNW, if anything it's smart on their part.

The current GNW system punishes successful groups that are large and active and rewards weak/almost dead groups.

Even smarter is if that 4th group has less than 9 active members because even coming 4th gets you packs and no one would need to go without them ever while also putting zero effort into GNW.