I don't think it's quite right to say that communism has never been achieved, surely the communes of Germany, France and the USA are pretty good examples of people living in a classless, leaderless society with shared ownership?
The problem, as with all forms of government is what happens when too many people get involved. Life on a commune depends on members of the group adhering to one broadly consensual direction, you just don't get that in a nation of 1.3bn people (or 300million in the case of the USSR) without extreme, draconian leadership debasing everything the idea of communism stands for.
The only way the Soviet Union could have worked and remained communist is if instead of being made up of 15 republics it was made up of several hundred thousand communes, with the central government acting only as a night-watchman government concerned with communal defence.
The co-operative movement shows that successful, profitable urban 'communes' can work.
Unfortunately, this idealistic state is impossible because there will always be people unwilling to stop taking advantage/controlling others.