Your source is an opinion article in an outlet deemed right-biased and of mixed factual reporting.

https://mediabiasfactcheck.com/washington-examiner/

"In the early 1900s, the AMA lobbied lawmakers to shut down many medical schools."

That's over 100 years ago. No information is provided as to which schools, or what the AMA's reasoning was behind their decision.

Likewise, lobbying to reduce residencies occurred over 20 years ago. The actual reductions were implemented by a Republican Congress and the Clinton administration.

"At the time, they argued there was an impending 'glut' of physicians. It is more likely they were, again, trying to protect their high wages."

Needless to say, that latter assertion is not in any way supported by documentation.