It was for cider. They drank a staggering amount of beer, cider and rum on a daily basis in the early 1800's. Cider consumption per capita in the was around 15 gallons/year. They drank even more beer and rum. They were also drinking around 5 gallons/year of distilled spirits.

Most people were what we would classify as functional alcoholics today.

Primarily for cider. Of which you can make vinegar, but that was not the primary reason. It was cider, which was the most popular drink in colonial/early US.

If you know what brewing with apples and not having access to modern equipment, sanitation and yeast is like then I highly doubt they were in short supply of vinegar.