Why does communism exist?

in XIX century several authors inspired by social conditions created by the industrial revolution elaborated theories about future scenariOS in which masive groups of people suffering the same problems become a political actor to achieve the power on their nations. it become real in Russia by 1917 leaded by Lenin and so on. whenever similar ideologically policital actors achieve power imitated lenin model (real socialism) but by the end of the 70s china started his onw way. there is few real socialism in the work today after its Europe collapse and Global mind, Earth Inc., etc