Dashes are used instead of parentheses or commas in the sentence because of the following reasons:
-Parentheses are used to set off a participle word or words which can be omitted, but does not affect the whole thought of the sentence. In addition, parentheses could also be used to add a specific detail about the word beside it.
-Dashes, just like parentheses, are used to set additional information off. Dashes are commonly used if the words it enclosed already has a comma or commas in it, just to avoid confusion. In addition, dashes are more appropriate to use for interrupted sentences.
