system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why didn't America stick with the Westminster model when choosing how to run a government?
gpt
Because each State in the Union was a sovereign entity that chose to create a federation to increase total military strength and trade negotiation power with other nations. They only gave up a part of their sovereignty to this federal government. 

In the Westminster model Power starts at the top "national level" and is then rationed out at different rates to the units making up that nation. It means that the member countries/entities of the union are not sovereign because the power does not start with them, it is granted to them.