ASCII isn’t just a “character representation” though. It includes code points for data serialisation and transmission control. You can represent tables in ASCII without resorting to printable characters nor white space as field separators.
I don’t why POSIX tools don’t already do this but I suspect it’s because most tools would have evolved by accident rather than being designed from the ground up with edge cases in mind.
Unix tools standardized a character representation (e.g. everything is ascii). The next step is a unified standard the syntactical representation.