Plenty of cultures are myopic: I know some folks who lived in Korea for a while who would complain about web sites that only allowed four characters. Most family names are 1-2 Hangul characters:
US-ASCII predates the internet, UNIX, WWW and almost anything else you currently use. While seminal, it was certainly not prescient. Now it is little more than a fun artifact to play around with: https://every.sdf.org/
US-ASCII predates those things in the US. In most other places, different alphabets predated ASCII, and indeed the US. Sort-of-old is no argument for quality or fitness for every purpose.
This is not about alphabets or character sets. It is about the first standardized computer-to-computer textual protocol. And that is US-ASCII. That it is all skewed to US characters is a derivative of where it was initially developed. But not to worry, zillions of other code pages for every language on the planet soon appeared, and yours probably included...
I don't disagree that it was the first computer text protocol, I disagree that "128 character US-ASCII is fundamental" nowadays, or (from article) "ASCII text remains the universal interface", or "Use only plain ASCII text. (...) The lowest common denominator -- i.e. ASCII -- will do just fine."
This is incredibly Anglo-centric and just plain wrong. It works fine as long as your colleagues are all named James, John, or Mike, but breaks down immediately once you meet a Françoise, Rémi, Cláudio, etc.
Even the IETF's RFCs, arguably the most popular plain-text documents on the internet, explicitly allows non-ASCII characters. Because the internet is global and unicode exists.
Most of us have encountered the "please enter a valid name" after filling in a form.