It's... complicated. The "whys" of MOL remain rather murky, 60 years after the facts...
- 12/1963 The non-NRO "white" USAF wanted astronauts, but DynaSoar had just been shot down, so they got a space station as a consolation prize
- From 1963 to 1965 USAF didn't really knew what useful military missions it could do.
See here -
https://forum.nasaspaceflight.com/index.php?topic=23864.880
- By 1965 the "black" Air Force - NRO program A - came to the rescue: "manned spysat".
- so it got a Key Hole number: KH-10.
- next, among robotic spysats, it was found it could do (on paper at least) a few things
a) Screw cloud cover: don't waste film
b) Watch for targets of opportunity
c) Very high resolution, (VHR) details as small as 4 inches
d) Arms control
maybe ? (I've seen a few documents related to that in the NRO archive)
And so it began for real, in summer 1965 after LBJ granted his approval. But there were grave doubts about its true usefulness and pertinence. Even more when in 66-67 GAMBIT switched from KH-7 to KH-8, and started getting ground resolution records after records. A decade later it returned a picture with details as small as 2.3 inches: 6 cm. Somewhat loosely related to this by 1966 an unmanned MOL was designed, also for the VHR mission.
Meanwhile CORONA successor evolved into the monster KH-9 (IOC 1971) which competed for funding with the equally expensive KH-10. By spring 1969 it was obvious not both could be funded, the debate went as high as Nixon himself. Which canned the KH-9 first, then reversed his decision, and MOL was dead on June 10, 1969.