Am I remembering right that we never see a vehicle get "possessed" while a driver was behind the wheel? Aside from the kid on the bike (which could equally be a legitimate crash rather than the bike flipping him on purpose)?
Although this isn't a movie where one should worry about logic, I think the best explanation is that whatever was taking remote control of machinery didn't want to "fight" a human operator, hence only vehicles that were unmanned became possessed.
It might be worth noting that even the electric carving knife "came to life" sitting on the bench, not in anyone's hands... Same for all the guns in the movie.