Earlier quoted context omitted.
It's not done for "PR". US hospitals are required to treat emergency cases, by law. The Emergency Medical Treatment and Active Labor Act[0], passed under President Reagan, codifies the mandate. (This is, to my mind, what caused the United States to end up with socialized medicine-- albeit a socialized medicine system where we don't get to have public discourse about how it works.) [0] https://en.wikipedia.org/wiki/Em…
We don't have "socialized medicine". You can go to the ER without insurance and with signs & symptoms of a heart attack and they'll try to keep you from dying, but they won't give you the triple-bypass and medicine you need to keep it from happening again in a month—unless they think you'll be able to pay for it.
Uninsured and under-insured people are cited as one reason why treatment costs are so high. Whether these cases actually contribute to costs in a substantive way doesn't stop the mandate to provide free emergency care being used as a political football.