Why did the U.S.S.R. become a totalitarian state?
Perhaps the best answer to this question is to reconsider the nature of the question itself. Russia under the czars had been an absolute monarchy, rather than a constitutionally limited monarchy like the British one. After the Russian revolution, there was an economic shift from feudalism to communism, that gradually declined into the oligarchic kleptocracy currently in place, but there really was never a period in Russian or Soviet history with an open system of government. Thus rather than becoming totalitarian, one should say it simply remained so, albeit with periods of more or less openness under perestroika and such.