Same for Lambic. For cheese and alcohol the region is important. All of these products have micro cultures or yeast in them. For Lambic, it’s a naturally occurring yeast. If they allow other beers to be produced in that region, then the commercial yeasts will dominate the natural Lambic yeasts in the finished product, and you will end up with a different end result. So the regional specification is a quality control method to ensure you get the exact same microbiology as has been used for hundreds of years.