Because USA have not technology to land a probe that has to land going backwards. Pure and simple.

NASA Langley Research Center's Contributions to the Apollo Program
The Lunar Excursion Module Simulator here at Langley's Lunar Landing Research Facility enabled astronauts to practice landing on the lunar surface. This training gave Neil Armstrong, Alan Shepard and other Apollo astronauts the opportunity to study and safely overcome problems that could have occurred during the final 150-foot descent to the surface of the moon.

Originally posted by QBSneak000
reply to post by Big-Brain

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Um....hate to break it to you but sure they have the tech. How about aircraft like the harrier to start with. Not to mention Mars' gravity is slightly less than ours. Oh and I almost forgot the lunar lander....sure, not much gravity there but still the same concept.

To cater for jet-borne flight, where the aerodynamic forces on the conventional surfaces are reduced or eliminated, a system of air jet reaction control valves are utilised. These are placed in the extreme nose, tail and at the wingtips to provide pitch, roll and yaw control. The system uses air bled from the high-pressure compressor of the engine and the valves are opened using pilot commands from his normal controls. Indeed, the valves at the wingtips and in the tail are directly linked to the aileron, tailplane and rudder so that when each of these surfaces moves its corresponding valve also opens. This occurs during both wing and jet-borne flight, but as the engine bleed is only operative when the main engine nozzles are vectored below 20 degrees no jet reaction force is produced unless the aircraft is partially jet-borne. The interlinking of the aerodynamic and reaction controls, allied to the progressive increase in the amount of air bled from the engine with increasing nozzle vectoring above 20 degrees, ensures that the aircraft is fully controllable at all airspeeds and during transition.

Originally posted by defcon5
This epitomizes how silly this thread is. The Lunar Module Simulator at Langley was so the Astronauts could practice landing, not to test if the LEM would work:

NASA Langley Research Center's Contributions to the Apollo Program
The Lunar Excursion Module Simulator here at Langley's Lunar Landing Research Facility enabled astronauts to practice landing on the lunar surface. This training gave Neil Armstrong, Alan Shepard and other Apollo astronauts the opportunity to study and safely overcome problems that could have occurred during the final 150-foot descent to the surface of the moon.