Hubble was the result of an open competition between a variety of companies and technologies. But the winners were the people who built the KH-11 spy satellite, who could offer the cheapest and best proved options because of their experience with KEENAN.
Both KH-11 and Hubble had similar sized mirrors, but that wasn't because of design reuse, it was because that was the biggest primary mirror you could fit in the Space Shuttle cargo bay (1). In actual fact no KH-11 went into space on a Shuttle, but the plan up until the Challenger disaster had been for the STS to carry all US satellites into space, including the KH-11, which was designed around that cargo bay.
1: The space shuttle cargo bay was sized the way it was for NRO payloads, but it seems clear that the USAF wasn't thinking about KEEENAN when they requested that size- a design like that would be better if it was wider and didn't need to be nearly as long. My suspicion is, when NASA asked them what size they wanted for the bay, they took the last design they had- the just cancelled KH-10 Manned Orbiting Laboratory, and used that.
Both KH-11 and Hubble had similar sized mirrors, but that wasn't because of design reuse, it was because that was the biggest primary mirror you could fit in the Space Shuttle cargo bay (1). In actual fact no KH-11 went into space on a Shuttle, but the plan up until the Challenger disaster had been for the STS to carry all US satellites into space, including the KH-11, which was designed around that cargo bay.
1: The space shuttle cargo bay was sized the way it was for NRO payloads, but it seems clear that the USAF wasn't thinking about KEEENAN when they requested that size- a design like that would be better if it was wider and didn't need to be nearly as long. My suspicion is, when NASA asked them what size they wanted for the bay, they took the last design they had- the just cancelled KH-10 Manned Orbiting Laboratory, and used that.