I think you misunderstood the letter: they aren’t complaining about Instagram specifically, they are complaining about a proposed version of Instagram designed

I think you misunderstood the letter: they aren’t complaining about Instagram specifically, they are complaining about a proposed version of Instagram designed for kids under 13. So your comment seems basically irrelevant to the matter - they aren’t asking him to change Instagram, they are asking him to cancel a product that hasn’t been launched yet.