What? Do you think cars can bounce a radar signal under the car in front of them to see the one in front of that one? And then the signal bounces back somehow? That's...not how radar works at all. Radar only estimates distances by bouncing the signal directly to and back from objects and it doesn't "point" the signal, which is why you need a number of sensors. They essentially triangulate signals to an object to determine where it is lateral to the car.
It is *literally* why Radar is limited...it can't possibly "see" things through or around any surface that bounces the signal, and that includes things like rain and snow (which is why most car radar systems will outright shut down if it's snowing or raining enough).