> that regulation or rule or something that makes it so like a hospital can't open too close to another hospital

You're referring to certificate of need laws, but it's worth pointing out that they're not universal. More than a dozen states have repealed them (or don't have them) and everywhere I've looked, there's strong evidence that their removal has increased healthcare access, which has put downward pressure on cost of service

> Another would be to just, train more doctors!

Bill Clinton placed a cap on GME funding in the 97 Balanced Budget Act, freezing the number of residency slots that the federal government would provide funding for, so this effectively froze the number of residents there could be, which effectively limits the number of doctors possible