Just opinion, but the US prioritized the Pacific war over Europe until the buildup for Normandy began The African-Italian campaign was not going to defeat Germany and the US leaders knew it. It's not clear Churchill did since it was his idea to invade Germany by way of Italy and Austria. This would place the allies in a better position to discourage Stalin, but discourage him form what? Eastern Europe is east of Austria and allied forces would have met Stalin after he occupied Eastern Europe anyway. Maybe Churchill was thinking of turning east from Austria and stopping the Russians while turning his back on Germany?