Why Stalinism and not Communism?

So, August 23rd is established as an international remembrance day for victims of totalitarianism. What immediately spoils the day for millions is the Stalinism term used in wording instead of Communism – Remembrance for Victims of Stalinism and Nazism.

Wasn’t Stalin just one of communist mass murderers out there? I’m sure everyone can name at least few others as well. Don’t they deserve to be mentioned as well or at least all of them combined into one word we all easily recognize?

What will history books write about it in 100 years from now, one wonders, if already today, for one reason or another, we can’t face the truth?