I’ve heard that people tend to drive more carelessly on good roads.
Driver fatigue is also a problem, and it wasn't until the last 20 years or so that driver fatigue in specific locations was considered as a possible cause of crashes. There was a fascinating story in Canada back in the late 1990s about a cluster of crashes in one location along Highway 401 between Montreal and Toronto. There were a bunch of crashes along one section about halfway between the two cities involving cars wandering out of their travel lanes or swerving off the road. They looked at all the usual probably causes: poor roadway geometry, distractions, animal crossings, etc. Nothing seemed out of the ordinary. Then they started looking at some of these crashes more closely and realized that driver fatigue was the most likely cause. The crashes occurred roughly around the midpoint between the two cities, at a time when a traveler between the two cities would be at around the 2.5-hour to 3-hour point on a 5-6 hour trip. They concluded that most of these crashes involved drivers who had either fallen asleep behind the wheel or simply "zoned out" on a dull stretch of road between two major urban areas.