Why don't *small* electric cars use small cheap hobby motors?
Power is not the only parameter of the engine. It also matters

How fast does it need to spin to deliver this power? Slow and strong engines need more windings than weaker yet fast (power is the same).
How well can it move from place a standing car? The engine you address is a propeller engine for a model aircraft.
How much cooling is required? An open aircraft engine is easier to cool.
For how long can it work fully loaded? For a model aircraft, it may be ok to replace the engine after maybe days of heavy flying if not earlier. Even cheap car is expected to last much longer.

This may explain the differences in size, complexity and price. Also, 1 hp is a surprisingly weak engine even for a small motorbike.