Cars get stuck due to stumps that are unable to be removed therefore rendering the car completely useless.

In real life you can get rid of stumps in multiple ways, with an axe, a hatchet if you have the time, a pickaxe (You dig around it and then break the roots), and more.

But for some stupid reason BI has decided this shouldn't be able to be done in game, and doesn't register the stumps as entirely collidable objects in game if the player swings an axe, hatchet, or knife at them.