>>12002329Well, firstly, because the A-12 beat out the more complex but stealthier Convair Kingfish design in 1959 only for Gary Powers's U-2 to be shot down the next year, which kicked off the interest in low observability for real and got us the Boeing Quiet Bird and that Teledyne-Ryan AQM-91. It's very likely that the CIA was also interested in VLO/stealth technology after the Gary Powers incident.
Secondly, because the A-12 was only in service for 5 years before it was retired with no replacement lined up. Electro-optical reconnaissance satellites that could return imagery as quickly as a spyplane weren't operational until 1980 or so when the first KH-11 constellation was completed by the NRO, and in 1968, imaging sats were limited to film-based designs like Corona or the KH-8 Gambit family that dropped buckets of film in re-entry vehicles and could only return imagery days/weeks after it was taken in stead of hours afterwards like the A-12 or the KH-11 could. That the A-12 was retired by the CIA after only 5 years at the height of the Cold War when they didn't have anything to replace it seems highly suspect.
Furthermore, the SR-71 wasn't a direct replacement, either, as it had a very different camera/radar setup built more around wide-area mapping, as the "Strategic Reconnaissance" designation indicated, compared to the A-12, which carried a single, massive, high-resolution camera like the one in the U-2. Using NRO satellites as an example, the A-12 was analogous to the KH-8 Gambit or the KH-11 Kennan families of satellites, while the SR-71 was more like the KH-9 Hexagon satellite.
