Because "they", the people that dislike the bridge, are in the minority with their viewpoint. And either they are right, and the bridge design is bad or they are wrong and the bridge design is good.
In polite normal society, if ones viewpoint is in the minority then it is incumbent upon those holding the minor viewpoint to apologize. If they are actually in the right, this is an apology a la Aristotle - an explanation of the position that goes against the majority and a refutation of the majority position. If the minor viewpoint held is actually wrong, then a mea culpa is required. Either way, the minority view requires the explanation.
That the bridge design is bad is the minority view (
here) (
here) (
here). If the viewholder still believes this position to be accurate, then that needs be explained. If the position is no longer held, then an apology asking for forgiveness for the incorrect view is given. These methods of interaction between polite normal people have been in place for thousands of years, and have served us well thus far.