In case you are interested here is a site were you can purchase very beer glass from Belgium.
https://belgiuminabox.com/shop/398-belgian-beer-glassware#/page-2/weight-0.12-4
More than 25 years ago the glasses were even more beautiful, but there was always a major problem with theft, from Belgium cafes, I'm ashamed to say mostly in the day by Dutch visitors.
In those days some of the breweries had fantastic bottles, one brewery had a bottle with three different coloured glass, like a church window. These types of bottles are no longer made, it's the cost, plus they were never returned to the breweries.
It's not really that they produce the glasses first, it's the time that they take to produce, the factory has to have a head start. The glasses have to be in place before the launch of the new beer.