Their guts press against the steering wheel, so it's harder for them to control the car. They often have the seat farther back than they should to make more room for their gut, resulting in them barely being able to reach the pedals. Plus they're almost always eating something while driving, so they're distracted and driving with one hand, or their knees or elbows. They're completely unconcerned with safety, all that matters is maintaining that caloric surplus.