I feel like this frequent---and, imho, overused---practice of "mdashing" is just a sneaky way of avoiding parentheticals (yet not their downsides, innately overcomplicating the task of reading---or enjoying---an otherwise immodest sentence) by dragging it beyond the point of necessity, wrought largely by a simple love of language---in and of itself a commendable sense---as simply an ineffectual tool meant to convey technical concepts to an audience lacking PhDs in linguistics.