Why? Because the ‘Era of Stagnation’ had gripped Russia’s economy, threatening its superpower status, the reversing of the economic decline and streamline government bureaucracy, communism failed in most areas, the war in Afghanistan, the end of the Cold War, Chernobyl, and the attempted coup and the rise of Yeltsin.
But the only country I can recall that is still communist is Vietnam
https://www.historyhit.com/what-were-the-key-causes-of-the-collapse-of-communism/
https://www.bbc.com/news/world-asia-pacific-16567315