At the time, it was a top-secret government project. That plane was the best spy resource our government had. We did not want the plane, nor its designs falling into the hands of others.
To prevent them from falling into the wrong hands and another nation building an SR-71:
> In 1968, a presidential order required that all molds and tools used to build the SR-71 be destroyed so that the plane could never be built by anyone again. This also meant that spare parts could not be made, so if there were any major problems, planes in storage would have to be cannibalized.
http://www.strategic-air-command.com/aircraft/reconnaissance...
> 8. How many SR-71's were built? 50 Blackbird airframes of various designations. The dies or molds were destroyed as directed by then Secretary of Defense McNamara to prevent any other nation from building the aircraft.
http://www.wvi.com/~sr71webmaster/srqt~1.htm
At the time, it was a top-secret government project. That plane was the best spy resource our government had. We did not want the plane, nor its designs falling into the hands of others.
That's pretty much my presumption. Really hard to leak something (or photographs, or schematics, etc.) which doesn't exist.
I thought about it, and I'm still waiting for someone to answer this. Good question.
To prevent them from falling into the wrong hands and another nation building an SR-71:
> In 1968, a presidential order required that all molds and tools used to build the SR-71 be destroyed so that the plane could never be built by anyone again. This also meant that spare parts could not be made, so if there were any major problems, planes in storage would have to be cannibalized. http://www.strategic-air-command.com/aircraft/reconnaissance...
> 8. How many SR-71's were built? 50 Blackbird airframes of various designations. The dies or molds were destroyed as directed by then Secretary of Defense McNamara to prevent any other nation from building the aircraft. http://www.wvi.com/~sr71webmaster/srqt~1.htm