I personally understand this change because it "protects" templates and you can do more with them in the future.
We all want CSS and JS optimization after all, right?
However...
I agree that it makes editing a theme a bit difficult, if only because I sometimes need to look at core.css or framework.css to "make sure" if this or that class is responsible for it. Let's say that I want to make sure and see which class is responsible for the light background or, for example, check what tables I can use (messages.css), etc., so far I have checked it directly in the file, which was convenient and quick. Yes, I know that I can check it in the console or in the documentation,but it's about convenience and the fact that it used to take much less time.