It was a cumulative process. We can look as far back as the succession system post-Lenin: there was a fundamental clash between Stalin and Trotsky. Socialism in one country, where the USSR wished to preserve itself and create buffers, espoused by Stalin, and Permenant Revolution, which wished to foster socialist revolutions around the world, espoused by Trotsky. Unfortunately, most contemporary revolutionary movements were unsuccessful.

Stalin and his allies slowly stripped Trotsky of his positions, eventually exiling him. Stalin, the ruthless politician that he was, annihilated his former allies. He was now an autocrat, but he presided over a country devastated by the recent Russian Civil War, and a system they called War Communism. A few purges, forced industrialisation programmes and man made genocides later, the Soviet Union of World War Two was created.

Whilst not very efficient, the sheer numbers they mustered into industry and the military gave them an advantage. Stalin died in the 50s, and Kruschev, his successor, tried to destalinise the country. He was eventually removed, and Brezhnev was the new leader. He was a stalinist, and undid many of the progressive changes that Kruschev implemented. His tenure saw the beginnings and developments of the War in Afghanistan, the Russian alcohol problem, and stagnation. Even worse was the corruption that fostered under Breznhev, with incompetent moscow bureaucrats trying to manage collectivised farms hundreds or thousands of miles away. One end of the country didn't know what happened in the other; the only outside communication was with short distance radio waves.

Chernenko and Andropov came and went, and then came Gorbachev. He instituted sweeping changes. Perestroika liberated the markets, Glasnost liberated the minds, and his constitutional amendments removed the monopoly of the communist party. Youth membership, as a result, plummeted into the ground. Although Gorbachev oversaw the USSR leaving their active role in Afghanistan, and the decommission of the Berlin Wall, he also was present for new instability. The elite did not like his changes, and they formed an emergency committee. As the USSR neared its end date, all of its problem came to a head. Gorbachev had referendums to retain a reformed Soviet Union, which numerous countries boycotted. The Baltic nations declared their independence, and the so called Emergency Committee attempted to hold a coup. After their failure, Gorbachev announced that he would no longer be serving as any sort of Soviet position. Every nation except Russia had referendums on leaving, and Boris Yeltsin took over in Russia, creating it as the independent Russian Federation, a member state of the CIS, thus ending the Soviet Union.

This question might be more accurately phrased as why did Russia transition from capitalist statism to state capitalism.

The only actual communism that Russia saw was during the revolution, when workers took control of factories and landed estates and governed them autonomously - these autonomous, networked organizations were the Soviets. The Bolsheviks promptly took control of the Soviets, killed anyone who resisted them, and forced the rest into a system that they modelled after Germany's industrial capitalist system while calling themselves communist.