It's probably a balancing issue where you could summon a bunch of demons, possess the car, drive it away/get depossessed, but still being able to mess with the survivors, I could see how it could get pretty unfair. Just don't waste all of your energy possessing their care if you don't have a plan.

What I do is plan their route. If they need to take bluff road bridge then I can set an ambush, then possess the car when it goes over it. They'll immediately trigger the traps if they exit the car on top of then. Or if they take off road then immediately start ambushing them once they inevitably flip the car or hit a bunch of trees. The car can still be broken. If they somehow manage to avoid all of this then they just played well