Those distributorships are coveted like taxi medallions for much the same reason.
New Glarus probably doesn't have the capacity to get a contract with a big distributor, and/or won't lower the price enough to allow the monopoly distributors to add the huge markup they're looking for or won't pay kickbacks, etc.
Back in the 80s I was stationed in North Dakota. The alcohol at the base store was purchased through a distribution system set up similar to the Commissaries and Exchanges and the prices were pretty good. There were one or two distributors in all of North Dakota and they looked with envy at the two Air Force bases because they did not have contracts with the military system.
Senator Dorgan, IIRC, rammed a bill through Congress and into law that forced military bases to purchase from the local distributors which included the state and local tax stamps.
The price of alcohol went up quite a bit after that and I always wondered how much money that worthless politician got back from those distributors.