It would make sense that the holes were a convenient way of thinking and speaking about large quantities of goods such that tribes of people might want to exchange. It would be a very visual way of comparing dissimilar goods, like "1 hole has 50 alpaca skins and I need 200 for the shelter I'm planning to build, so I need 4" and "1 hole has 8 baskets of dried fish which can last 3 families thru the winter, so I need 3 for the nine families on the farm", etc.

And I bet they paid a bit of rent for the privilege. Pretty cool.