Why do you think the delegates at Versailles refused to allow German delegation

When the treaty of Versailles was negotiated (without the Germans mind you) they didn't refuse to allow German delegation. They didn't invite the Germans because they were under the impression that the Germans had surrendered (instead of the cease war that meant neither side won.) Since Germany had "lost," the loser had no say in the terms of the treaty and was forced to accept it.

The treaty of Versailles was one of the causes of World War II.