It's not obvious that a bicycle would be in any way better than a carriage. So it makes sense that people tried to improve carriages instead of single riders. If you ignore the pollution aspects of cars, and the problems caused by the sheer number of them, they are a superior mode of transport to bicycles. If I were a 1400s inventor, a 4 wheel carriage with pulleys would seem much more attractive than a 2 wheeled contraption which leaves me exposed to the elements.