Suppose a custom Racket reader accepts paint red blue as (paint red blue), ends the form at a newline, and treats # as a comment starter. Where must those whitespace and comment rules live?
The reader establishes the forms that reach the expander. An ordinary macro inside an existing language cannot retroactively change its surrounding lexical rules. A custom reader could own this notation, but it adds tooling and documentation obligations. For three words, keeping ordinary syntax may be the better tradeoff.
