The Greek campaign was mounted for strictly political reasons, because all the participants understood that the military side would be insufficient to make a difference. The problem was that Great Britain had repeatedly made guarantees about defending Greece and those guarantees had to be backed up with action. The British and Commonwealth leaders were concerned that they would lose prestige in the eyes of the Americans if they declined to aid Greece. The British Foreign Secretary, Anthony Eden, took the British obligation very seriously, even when the Greek leadership questions the wisdom of the British weakening the force in North Africa to aid Greece.
The Greek republicans, who were in opposition to the ruling monarchists, thought that Greece had made a weak response to the German attack. The charge was that the Greek monarchists, like the Yugoslav government, secretly admired the Nazis and wanted to join that side against the Allies. This is based on the account in Vol.II of the Australian Official History.