> Carrefour has stores in Italy and Spain.

And Auchan has stores in Spain (Alcampo).

I'm not saying that the boundary is a 20km high wall of fire nothing can go through.

I'm saying that:

1. the direction is mostly big countries -> smaller countries, and very rarely big countries -> other big countries or even rarer, smaller countries -> big countries.

2. 20+ years after the EU has started, the level of high level integration is still pitiful.

People don't want complete integration.

If I go into the Carrefour in Sallanches (FR) then I will buy a completely different set of products to those that I would buy in the Carrefour in Aosta (IT), the two are 80km apart, I have shopped in both multiple times.

I don't think the supermarket example really maps across to the subject of the linked article.