Common sense is so called because it is held by many people, common people of little or no importance, who are not in a position to make decisions. The more important one is, the more likely one is to be in a position to make decisions and the less common ones sense.
A proof of this is in the sense of importance held by those elected to government. They are so far removed from common people that almost no common sense is to be found amongst any of them.
The question of how common it is, is also an important part of the answer, the other part, is why is it not utilised? The inverse relationship of holders of common sense, to decision maker is the answer. HCS = 1 / DM;