Because when Italy surrendered in 1943 quite a few Italian units went over to the Allied side. The Italian Air force split in two at the armistice. The Royalist "Italian Co-Belligerent Air Force" (Aviazione Cobelligerante Italiana, or ACI) fought for the Allied forces. The Fascist "National Republican Air Force" (Aeronautica Nazionale Repubblicana, or ANR) continued to fight for the Axis. Historically the Italian forces in Greece and Dodacenes switched over to the Allied side and the Italian garrisons in the Dodacenes fought the Germans unsuccessfully. While the Germans already had a plan in place on mainland Greece and disarmed the Italian Garrisons quickly before they could do anything.