After several recent high-profile incidents, in which baseball fans have been struck and injured by foul balls in major league stadiums, two teams — the Chicago White Sox and Washington Nationals — announced that they would extend the protective netting in their respective parks, all the way to the two foul poles.These improvements are laudable; they also beg the questions: Why don’t the protective nets already extend farther and what should Major League Baseball and its member clubs do about it …