You can only practice medicine if you studied in the US. No doctor in the world can practice medicine in the US without having to re-certify their knowledge.

Also, education is closely tied with government funding, so it's impossible to bootstrap a college or university to cheapen the cost of education. Thus you can only go all-in to medschool. This is not 100% accurate, there are some alternatives like PA's and NP's. So the current system can absorb only so much.

There are also specific funding rules for residencies, which mean that the amount that is given is done based on gov funding.