People are lazy. The ASCII C0 separators -- FS, GS, RS, US -- are non-printable (by design), but this impacts their usability by laypeople, because they don't

People are lazy. The ASCII C0 separators -- FS, GS, RS, US -- are non-printable (by design), but this impacts their usability by laypeople, because they don't show up as obvious symbols in a plaintext editor, and most critically, they visually seem to be absent from keyboards, so additional domain knowledge is required for people to figure out how to produce them. So instead, people developed all sorts of formats that are subject to delimiter collision. Also, ASCII is recognized as a widely-deployed standard now, but this wasn't always the case. Computers used dozens of different codepages to represent characters with bytes, and while 26 English letters, 0-9, and some punctuation was always present, control characters seldom had equivalents in a different codepage, so interchange was a problem, because in most machines' native codepages, these delimiters were absent. ASCII actually abbreviates 'American Standard Code for Information Interchange', but it largely came to be used for printable characters only -- "plain text", and not as a format for structured data. Although by that point, the ship on C0 delimiters had largely sailed, to compound the chicken-and-egg problem, some codepages that were developed after ASCII often discarded the notion of control characters entirely, and redefined their byte sequences as additional printable characters. Windows-1252 was a notable offender [1]. [1] https://en.wikipedia.org/wiki/Windows-1252 https://en.wikipedia.org/wiki/Windows-1252