Why didnt kai and nya went to get the golden wepons in season 7 finale

Back in season 7 hands of time kai, nya and wu catch up with the time twins to stop them and get the reversal blade. Then after the time twins escaped after the battle on the monastary. after that the reversal blade was founed by nya then they went back before the twins could escape. my first thoght was why couldent they revers back days before, before the time twins got their so they could get the golden wepons and give them to the past elemental master of ice and light (and probly young wu...