פירוש על עבודה זרה 93:11

The answer is provided by noticing the difference between cases where this concept leads to a leniency and cases where it leads to a stringency. In the case of the blood, it would lead to a leniency—if the wind covered and then uncovered the blood, the notion of “disqualification” would lead us to conclude that the blood need not be covered again. Since it would lead to a leniency R. Papa did not invoke it. But maybe he would invoke the principle in the case of the lulav, for there it would lead to a stringency—once the tree was worshipped its branches cannot be used, even if the tree was annulled as an idol. Or maybe he would never invoke the principle, no matter the results.
Since we don’t know whether R. Papa did invoke the principle to lead to a stringency, the question had to be asked. But, as often is the case, there is no answer.