A typical car engine has four cylinders, the graph of torque output verses revolution is virtually a saw-tooth occupying less than half a revolution. This intermittent output means that it cannot run slowly and certainly cannot re-start itself without an electric motor. Why not ditch the poor old petrol or diesel engine and stick with an electric motor in the first place?
An electric motor suitable for powering a car needs to be no bigger than a biscuit tin and has just two bearings. The electronics needed to drive it is the size of a suit case. Just compare that with the poor old combustion engine. The huge block is almost hidden by the rats nest of pipes required to allow it to comply with emissions regulations.
If the combustion engine was invented today, I doubt that any manufacturer would consider developing the poor old thing, such is its complexity.