I also appreciate that they did not attempt to tackle filesystem encoding here, which is a separate issue that drives me nuts, but separately.
For example, on Unix/Linux, using iso-8859-1 was common when using Western-European languages, and in Europe it became common to switch to iso-8859-15 after the Euro was introduced, because it contained the € symbol. UTF-8 only began to work flawlessly in the later aughts. Debian switched to it as the default with the Etch release in 2010.
IIRC, the main way this brittleness bit me was that every time a buffer containing a non-ASCII character was saved, Emacs would engage me in a conversation (which I found tedious and distracting) about what coding system I would like to use to save the file, and I never found a sane way to configure it to avoid such conversations even after spending hours learning about how Emacs does coding systems: I simply had to wait (a year or 3) for a new version of Emacs in which the code for saving buffers worked better.
I think some people like engaging in these conversations with their computers even though the conversations are very boring and repetitive and that such conversation-likers are numerous among Emacs users or at least Emacs maintainers.