Ok - the bolded part is where I’m seeing the disconnect here.
If you had read the books, you would know this. I know you haven’t, so I’ll explain to you what you’ve got mistaken (and I understand that it wasn’t clear in the film, but as the film was self-evidently based upon a book, I have to assume that the film wasn’t trying to change the backstory it was based on, as it didn’t try to change anything else).
In the books, there was a long-ago disaster (speculated to be environmental, but largely left to the imagination of the reader) that rendered large parts of the American continent uninhabitable. The implication is that the centers of power all collapsed/were destroyed/were abandoned, and a new country - Panem - formed from the remaining few livable parts of the landscape.
This new country was comprised of a Capitol (presumed to be in the Rocky Mountains) and a set of 13 Districts scattered throughout the country in various places to perform supporting roles (fishing, mechanics, mining, etc). It was at THIS POINT - way before the time period of the book (and film) that the Constitution and the USA were lost.
Over a long period of time (anywhere from 50 to several hundred years is possible, but no specifics were offered by the author), that Capitol got greedy, and the Districts began to be oppressed and treated as second-class citizens. The oppression eventually got so bad that the Districts rebelled, the Capitol squashed them all, bombed one District entirely out of existance as a warning to the rest, who surrendered, and who live now under constant surveillance and armed guard.
The books begin 75 years AFTER that rebellion, and possibly several hundred years AFTER the dissolution of the USA into this successor Panem - a smaller, central-powered country. The Capitol hasn’t changed any from the beginning of Panem’s existance, because it didn’t have to - it began as a country purposefully as a centralized power with outlying support districts. Later, after the oppression of the Districts caused a rebellion, it still didn’t need to change - it simply defeated the rebels and kept on going.
The author has specifically stated that she based the idea of the country on Rome and how it treated people from all of its conquest areas - to Romans, Rome was the only important place, and everything else existed to support that idea.
I can easily see how this information didn’t get conveyed in the film, but for people who read the book(s) it is a little insulting to insist that the film (and the source material) are referring to specific things that don’t make as much sense when all of the source material is considered. You are welcome to your opinion, of course, and if that particular meaning resonates with you, you are welcome to consider the movie with that interpretation - people are looking at it with all sorts of interpretations.
I just wanted to let you know some of the background knowledge you are missing, so you could maybe understand better where the people disagreeing with you are coming from.