Why didn't the Arashiyama team just deactivate and reactivate their triggers during ep 15?
The possibility of a trap, and the training they received.

Think about it, when is the best time to attack?

When the enemy can't defend.

They had no idea if they were being watched, and since it takes only a split second for someone with chameleon to hold a trion blade to their throat, it would make no sense to risk turning human.