Real Canadian Superstore review: Self checkout

I went to Superstore (Moosejaw) yesterday to pick up groceries for Instacart. When I arrived at the self-service checkout, the employee rudely informed me that Instacart customers are not permitted to use it. So, I'm curious as to why Instacart users are not permitted to use self-service checkout. Is there a good reason for this? They didn't give me any explanation. Is there a special policy for Instacart customers at Superstore? Also, there was no sign at Self Checkout indicating that Instacart was not permitted. I simply wanted to know why I was denied self-service checkout. Furthermore, I was not treated well there. Is this how the superstore treats its customers?