Because other teams will develop plans specifically to counter Frankie Hejduk. You cannot stop Frankie Hejduk, you can only hope to contain him.
Well, according to this, they might need to be preparing for Chris Klein instead. http://ussoccerplayers.com/latest_soccer_news/506380.html Maybe that's why Bruce keeps our roster secret - so they can't prepare for our unknown, surprise attack.