You're understanding is very poor.
Literally thousands of people who go to medical school in India start residency in the US every year. In fact, >7,000 foreign medical graduates (both US citizens and non-citizens) started PGY1 positions in 2017 (most recent year for which we have complete data).
https://www.acgme.org/About-Us/Publ...Graduate-Medical-Education-Data-Resource-Book
This is because the US medical training system (i.e. residency programs) requires >7,000 more people every year than the US medical education system (MD and DO schools combined) provides. 2500-3000 of these are US-IMGs (mostly Caribbean grads) and the rest are foreign-IMGs (majority from India).
Caribbean medical schools exist because of the deficiencies of the US medical education system. Plain and simple.
It's asinine that thousands of US citizens, who are willing and able to become physicians, must go outside the US for medical education every year for no other reason than the powers that be for US MD/DO schools refuse to increase enrollment.