I think it is West's fault. On the first trick, with clearly so many hearts to choose from, East played his very lowest one, suggesting a club feature. From West's perspective, if it is a void or the ace, a club play cannot hurt: we are going to take take 2 clubs and two hearts or two hearts, a club, and a club ruff. But, if West had diamond cards (say KTxx) but no club help, the defense needs to setup the diamonds before the club ace is knocked out. For example, if south has KQxxxx xx Qx KJx The defense needs to play two rounds of hearts then a diamond.