Electric car motors enhanced

  Currently electric cars use one big motor to run all four wheels as a replacement of the engine. Why don't they use 4 DC brushless motors? 1 on each wheel would make the car more efficient, also using fuel cell stacks would solve power problems, plus because there DC brushless heat output would be reduced.
  My theory is that a dc motor could be made so that the middle bit with the turns of wire could be inside the wheel itself with an outer casing with the magnets on that the final wheel and tire bolts onto. This would allow for a relatively simple conversion from internal combustion to electric.
  I have 3d models and image if you want them.