Hahaha, I thought you would say that. I can't say whether that is true or not, but, I am very doubtful that they hate you.
And well, the GMs (by picking the teams) assume leadership role as this is last TEAM standing. A team without a leader= fail. Every time I've participated in this event with the passive GM as my team leader, it's always lost. And vise versa. While GM's are not allowed to participate themselves in combat, they are allowed to give out basic orders. I think even the basics go a long way.
They could give up their roles as the leaders of each team by passing it on to another player.. maybe. However, I do think it would be a more successful event if more time was spent in creating order and a plan to win.. rather than as you say battling it out like orcs vs footmen. (Oh, and taking 20 minutes to pick the teams.)