They are valid within macros (e.g. they would match a pair of sequential tts instead of just a single one) and are emanated as separate tokens by the parser rather than a single one so that |> is indistinguishable from | >. Changing that would be technically a backward-compatibility hazard with macros AFAICS. Not sure how serious, though; would require at least a crater run to check.
But perhaps you’re suggesting that this token sequence could still be used for this purpose? Someone who knows the compiler better than me might be able to comment on that.