system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does milk come in gallons and soda in liters (in America)
gpt
Because the soda bottle was created after the US government went metric, but milk already came in gallon jugs before US independence.

Essentially there’s no law dictating what private companies use, but the FDA works in metric, and US imperial measures have to be converted back to the metric standard.  So for newer comestibles, it’s simpler just to go metric, while older ones are going to stick with existing supply lines and volumes customers are accustomed to.