But, correct me if I'm wrong, you need the forestry expansion for that? I know many departments that are forestry departments that still have the brush truck.
but it is just part of the game. Yes...in real life you do not have to be affiliated with "forestry" to have a brush truck. But in the game to purchase forestry equipment you just have to have the extension. And I suspect that if you do not have a "forestry" extension, no wildland or brush incidents will spawn.