All of these "You can't do X on my game" screeds on TTRPG books and the sycophants that push for this things are just part of the push to drive the creative GMs out of playing D&D, Pathfinder, etc.
I know that from an old timer's perspective these screeds seem silly and impossible to enforce but I'm not so sure that's really true. If you think of all the ways that people are introduced to new games (that aren't D&D), some of the main ones are: conventions, online gameplay, and people joining other groups. The game company can enforce their "You can't do X" rules on convention games, as they run them. They can also pressure RPG YouTubers to follow those guidelines. And for players joining games, these sort of meta-rules can set a certain expectation among players that those rules will be seriously followed, which puts pressure on GMs looking to add players to a game.
The only people that are immune are established groups which probably aren't changing systems very often and, thus, represent an insignificant portion of the potential customer base.
All in all, I think these types of playstyle enforcement rules are much more effective than people here give them credit for.