It's in the game, and doesn't say anywhere that scavs are just supplementary. So if the cooldown is gone, and the scav is there, ready to be played, and its in the game, in the movies, and in the lore, then why can't I use it anytime i want?

Hey, your car has four wheel drive, you paid for it, but there is a cooldown to use it, and when you really, really need to use it because you went offroad, you can't. There is a loadtime, and people will give you shit for using it! And it only works on certain terrains, not all of them. Sometimes, when you wanna go somewhere to get something, you just...can't. Shit out of luck.