I think it's the other way round: most employers are subject blind, only a few need you to have specific degrees: Medicine, Law, Accountancy, Actuary, etc.
Technical jobs like coding require you to demonstrate ability, and therefore many people who have a not-quite right degree (physics degree to be a coder) or even no degree can get the job.
"Technical jobs like coding require you to demonstrate ability".
Yet they test you on an hour and a half online "coding challenge", which is completely irrelevant to day to day work. I have been looking for a senior level job recently and only one place has actually asked me questions that I consider relevant. In another I had to calculate the inersection of two rectangles for a Django job. I managed it, but it has nothing to do with my coding ability, knowledge of Pythonic / Django ways of doing things or anything that I would be doing on a day to day basis.
Yes, there's a high false negative rate incurred by doing it this way. I know what you mean, I actually did the same question not long ago (given the 4 corners, return the intersection area), and I too think it's irrelevant.
But it is definitely the case that someone who can't code could not possibly pass this test.
Technical jobs like coding require you to demonstrate ability, and therefore many people who have a not-quite right degree (physics degree to be a coder) or even no degree can get the job.