The cost of making a shoe is in assembly, not the materials, and that doesn’t change much from size to size.
Width is very much a decision of the manufacturer, but the small sizing could be due to the factory using US-sized soles, and then the shoes are mis-converted from US sizes. In men’s shoes, a US 10 is a UK 9, but it’s not simply “subtract one”, because a US 11 is a UK 9.5. I generally use European sizes when I buy shoes, as there’s far less ambiguity involved, but even then my 45 could be a 44.5 or 45.5 depending on brand.
Shoes cannot be bought online with any kind of success - sizing is too variable, and it’s the one thing where you need a proper fit.