They damaged the illusion of the "B" in "BDFL" with their changes in 19. Open-Source programmers like to believe that their toolchains and whatnot are egalitarian, and treat everyone as equals. Many accept the idea that the STDlib will be "more special," because its included in every copy of the language. This pill is made easy to swallow by the idea that your code, for your tool or library or whatever else, can be just as powerful as a built-in bit of code.

Elm's maintaners decided to break this. They created what amounts to a caste system for code. If your code was blessed, then it got all sorts of extra abilities not granted to un-blessed code. And the sole authority on blessing was the cadre of developers.

Now, as to why they did this is a different discussion. There are good and bad arguments on both side. But as to why it comes up all the time? Ego