Because they cost so much and the air force could only afford 32.
It is the Lockheed SR-71 "Blackbird", a reconnaissance aircraft.
If you are refering to the SR71 blackbird, the military plane, it was designed and built by Lockheed Martin. The SR-71 Blackbird was built by the famous Lockhead "Shunk Works" Heading up the team was Clarence L. "Kelly" Johnson one of aviation's most important aircraft designers.
Only 32 were made. 12 were destroyed in accidents but none due to enemy action.
Boeing
What is SR71 auto insurance
The SR 71 was a very secret high speed, high altitude reconnaisance aircraft. Only 32 were built, at enormous cost.
Black
3.5
2193 mph
Stratosphere
2200 mph
the stratosphere!