They have special attributes which boost the Bolshevik war effort immensely.
Search the manual for the words "Trotsky only" and you will see what I mean
The tutorial shows how to see a general's special attributes in-game. With Lenin or Trotsky selected, click on their name at the listing at the bottom right of the screen. A rectangular screen will show up on the right of the screen, describing the guy. In the middle of it, after "Abilities:" are little icons. Put your mouse over each and you will discover what these guys can do.