It seems like a lot of reasons, many of which derived from hubris and a delusion that one can plan an entire society, and everything that follows from this mist

It seems like a lot of reasons, many of which derived from hubris and a delusion that one can plan an entire society, and everything that follows from this mistake. Bad economy, over reliance on limited set of heavy industries, corruption, lack of agency; overall reduced economic performance and thus unable to outcompete the US economy, which was forcing the Soviets into an arms race death march.