Why were all Germany's colonies given to other countries after World War I?

Britain and France had seized most of them in World War 1 and wanted to keep them. The victorious allies were keen to keep Germany weak after the devastation that had been caused in the "war to end all wars" and so Germany's overseas empire was confiscated. They were not keen on Germany being a world power, either.

The League of Nations (an early version of the UN), newly created and led by France and Britain, decided to split the German colonies between France and Britain, but they would not be classed as parts of their empire, instead they would be "protectorates".

The plan was for France and Britain to oversee and protect these territories while they built up their own government, the two empires could then make them fully independent.

As it turned out however this did not happen and the territories virtually became part of the British and French empires.