WW2 was a major factor as well. One could argue that despite appearances the Soviet Union never managed to completely recover from the horrendous losses suffered in that war - the loss of committed cadres, the loss of unstoppable can do optimism, the loss of innocence which made the leadership paranoid about security thus hampering a balanced economic development, every undertaking needing to simultaneously serve the secondary purpose of defence application. Had that war been won earlier, more decisively and at a fraction of the human and infrastructural cost things could have gone differently.