Why was the siviet union determined to keep hungary as a satellite?
1) Marxism is a universalist ideology, that is, Marxists believe that communism is inevitable for all countries. And, when all countries become communist, then all national differences will disappear. If Hungary fell to "counter-revolutionary, bourgeois elements" then the inevitable spread of Marxism could be under threat.
2) The Soviets fought tooth and nail to remove the Nazis from Hungary. The Battle of Budapest cost the Soviets 80,000 dead and nearly a quarter of a million wounded. They were not going to simply withdraw and hand the country over to their ideological enemies.