If it's so easy to solve for, why hasn't it happened already?

Because the US is no longer a full democracy, and the government mainly represents corporations rather than its citizens?

The Us has never been a democracy, it has always been a (democratic)republic.

It started as a democratic republic but it isn’t currently a democratic republic.

Democracy in the US has always been flawed. The situation has been steadily improving in some areas (voting rights) with set backs in other areas (gerrymandering, legalised bribery of politicians). There's a lot that needs to be done, but the US has always pointed in the direction of democracy.

At creation US leaders were selected from a subsection of the population in all land governed by the nation. With Puerto Rico, DC, etc that’s no longer the case making the US an empire not a republic.

Controlling who has the vote has long been an issue, but denying political power to a region is a different category of thing than denying it to poor people etc.

Maybe, but then the US is a weird kind of reverse-empire, because it's exactly the capital where people don't get to vote, at least for the senate. An empire is usually where only people from the core region have any representation (if anyone does, because I don't think empires need to be democratic at all).

People in the capital do vote, just in congress rather than the general population.

Being a republic has nothing whatsoever to do with being a democracy. They are orthogonal concepts.

One of the biggest issues that prevents this is that states cannot require residency requirements (e.g. must have lived in state for 2 years) as part of the criteria for access to such social safety nets.

https://en.wikipedia.org/wiki/Shapiro_v._Thompson