From my short experience with this - manufacturers want to ensure this internationally too. So then same product would cost around the same in Germany and in Poland. Otherwise Germans will check fit of shoes in German B&M store, then go buy it online from some Polish store for X% cheaper.

Manufacturer does not want that, because then it will lose most of it's distributors in Germany.

NB: Though I am not debating if it's right, fair or best for consumer. Just mentioning, what I've experienced.