I don't know of all of the laws of all the states or cities around, of course, but alcohol sales are weirdly regulated.
As an example, in a city in Wisconsin, I saw one of my favorite local brewpubs with their brewery wagon at a farmer's market. The brewpub is fully licensed, and has growler sales.
I went up to it and all they had was soda, and empty growlers. When I asked him why, he said it's against the city ordinance to sell alcohol/beer on the street or in public. But he was showing off empty growlers, that you could buy and then take to the brewery for filling.
Some states allow limited self-distribution for breweries, but others don't even allow nanos to self-distribute, so they have to sell their beer to a distributor and then buy it back to serve in their own taprooms.
It's not just the being a licensed brewery that would be a hurdle- then the laws about sales and distribution come into play. And of course, the whole "sell in public venues" issue.
Generally, wine and cider and mead don't have those same restrictions due to the three-tier distribution system with beer.
