I initially thought some one might have answered this question in the past, but in looking through my search results and the FAQ, I did not seem to find one.
If you walk in to any grocery, pharmacy, or convenience store today; you will find smaller bottles of soda in 12, 16, and 20 oz. However, once you go above 20 oz you are met with the ubiquitous 2-liter, the rarer 3-liter, and the and upcoming 1 and 1 1/2 liter bottles. These metric-based bottle sizes with the small exception of certain liquor bottle standards (250 ml, 750 ml, 1500 ml) stand in stark contrast to nearly every other beverage type (milk, orange juice) that get measured in ounces, pints, quarts, and gallons and of course all food-based product measurement sizes - a cup, ounces, etc.
So how did we get here?
7UP was the first major company to go metric. This was in 1974. There was a push on for the US to go metric. Companies wanted to be prepared in case the move was successful.
At the same time materials for the containers of soda and the like was rising.
7up found they could make a shorter, different shaped bottle that would be cheaper to make.
Faced with a problem of a shorter bottle being perceived as containing less liquid, 7up saw that the bottle would hold 2 liters of product. 2 liters being more than 2 quarts they could advertise they offered more product for less price.
Market liked the idea of getting a couple of ounces for free. The savings in packaging more than made up the cost of the extra soda.
https://www.gpo.gov/fdsys/pkg/STATUTE-89/pdf/STATUTE-89-Pg1007.pdf
http://object.cato.org/sites/cato.org/files/serials/files/regulation/1991/1/v14n1-5.pdf