Answer:
The most important reason is that the Communism meant the division of land, which until then was totally in the hands of rich Russian landowners.
Step-by-step explanation:
Most people in Russia, especially peasants were poor. They had no belongings and had to work on the farms of Russian landowners. Communism offer them distribution of land and end of war, during which Russia suffered the most. That is why many people accepted to join the Red Army.