Simple, when the Second World War ended the Nazis ended up as a political force, so anyone can accuse them and no one is going to defend them.
But the Communists continued as a political force, so in some way or another their atrocities have been defended by some idiots.
There approach and methods are being promoted and used by antifa. Not just defending the theory. They are out in the streets rioting and causing violence, in the name of their communist cause