The Sims 2 also had a chunk built into every lot that served as a carpool path, and later extended to additional pathing in the form of a driveway object which allowed cars to be fully animated.
This is a totally different setup than Sims 2, and a totally different setup than Sims 3 even. Roads in Sims 4 aren't roads, they are 3D objects built into the world mesh. There is pathing for vxf vehicles that travel down a predefined path at certain intervals on a never ending loop. There is no pathing for working vehicles that enter or exit the roadway, or even stop at a specific point along the roadway. With the disclosure that swimming outside of pools would require a brand new world asset to be created, it kind of goes without saying that this situation would also call for a new world asset to be made with specific pathing for vehicles. Thus containing whatever gameplay came with vehicles in one area as the animations and functionality wouldn't be compatible with previously released worlds.
I think they have better things to focus on in Sims 4.
