Comment by yieldcrv

A lack of competing forces

The US collectively felt that they needed to prove that capitalism was superior to communism. In this case, the contracting system was the competition between private sector entities to produce the parts and expertise, alongside NASA the state run enterprise handling requirements and coordination.

While the Soviet Union relied on more state run enterprises, aiming to prove collective coordination.

With the absence of resources up there, and lack of return, and inability to prove anything about capitalism vs communism to anyone that mattered, the programs atrophied in both unions.