Earlier quoted context omitted.
Also most languages already support nested clause structures without the use of parentheses.
They do, but there's a limit to how much recursive embedding the average reader can cope with, especially if the writer embeds a lot of modifying clauses in the middle of the main clause so the reader is left waiting for information they need to make sense of the sentence as a whole.
Parentheticals in English sit in this sort of midpoint between a modifying clause for necessary elaboration and a footnote/end-note for optional detail, and lots of people including me use parentheses where "inlining" the parentheses or moving them to a footnote would be more appropriate. That's in addition to conventional uses of parentheses, like to expand abbreviations.