Radiator in front?

Like many features of automotive design, it's a trade-off, based on packaging considerations. Computers embody similar compromises.

You want the radiator where it gets lots of cool airflow -- obviously, the easiest way to do that is to place it at the very front of the car.

Airflow in the wheel wells would not be as unobstructed, and as pointed out, leads to other problems. Two radiators just creates complications with lengthy plumbing and fan location. Sure it could be solved -- a lot of the mid-engine exotics have dual radiator inlets, but they are not engineered to a price point, either. And they don't care if a simple service procedure takes 14 hours of shop time.

Finally, I think your basic premise is somewhat off the mark -- a little warm air blowing over the outside of the engine probably has no effect on its internal temperature, compared to the total effect of the cooling system (the engine is liquid cooled, not air cooled). The exhaust manifolds are radiating heat into the engine compartment already. The issue with cool intake air for the carburetor can be solved without moving the radiator, merely by adding a cold air inlet from the grille area (as most modern cars do).