The DM is free to change any rule they want, but some may be reluctant to do so if the rules are clear and hard to argue. Some like the wiggle room, or doubt, to do as they please. It also grants more leeway to make determinations on the fly.
Some like black and white, while others like shades of grey. I prefer the level of abstraction or scope be set with any rule, and based on that, the rules are made as clear as possible. I do not believe building vagueness or obscurity in rules offers anything meaningful. That is even more evident if you are improving or clarifying existing rules which D&D has a long history. From a developer standpoint is appears they are looking for an excuse to go back to when the game first started, where there was no hindsight for comparison. Unfortunately, that is not possible with D&D in present times.
Some like black and white, while others like shades of grey. I prefer the level of abstraction or scope be set with any rule, and based on that, the rules are made as clear as possible. I do not believe building vagueness or obscurity in rules offers anything meaningful. That is even more evident if you are improving or clarifying existing rules which D&D has a long history. From a developer standpoint is appears they are looking for an excuse to go back to when the game first started, where there was no hindsight for comparison. Unfortunately, that is not possible with D&D in present times.