Not during residency, and I have not idea what the second part has to do with the match going underfilled. Are you saying med students saw this phenomena and decided emergency med was best left to PAs, and did not apply to match?

What I heard was emergency departments suffered brutally during covid, and that has had a chilling effect on anyone wanting to go into it. The med students matching now were all rotating through departments during covid.

yes, there are periodic oversupply and undersupply of various medical specialties (just like oil, labor, money, real estate agents), and medical students do react and choose accordingly. ER was hot for a while, and radiology was not so hot for a few years after 2008. Now surprisingly radiology has held up despite AI fears, because of baby boomers starting to get cancer, and ER is down, because private equity went nuts investing in urgent care centers before covid.