פירוש על עבודה זרה 10:8

The mishnah in Hullin referred to selling animals for food. The assumption is that people would buy the animal and slaughter it the same day. Our mishnah refers to sacrifice. People might by the animal three days ahead of time.

If the animal is being sold for sacrifice, then maybe the prohibition needs to be longer than three days. After all, Jews are supposed to start preparing for the Pesah sacrifice thirty days (or at least two weeks) before Pesah. The answer is that Jews need more time because there are more rules for us about what flaws disqualify animals from being sacrificed. Non-Jews have fewer rules and therefore three days is sufficient.