Actually there are some exceptions. Swiss, Norway and some other countries have a cross on their flags and sometimes on their jerseys. Turkey, Saudi and some Arab counties have the star and crescent on their flags and sometimes on their jerseys. FIFA don't tell them to cover it up.
Look, If the idea of the hijab is to prevent men from lusting then they in the wrong sport or from another planet. That is part of man's nature. Men are born natural lusters. It have men who does lust after Miss Piggy.