There is selective formation of keto-ketal 9 with the keto carbonyl on 8 due to the crowding of the methyl groups at the bottom of the cyclic structure and the selected group is a better protecting group. The characteristics of a good protecting group is that it selectively reacts with the group you wish to preserve, it adds easily and is removed easily. It must also survive subsequent reactions until it’s removed. So the other group wouldn’t be able to do that.