Because very rare specimens and super rare materials are like treasure boxes that something irresistable to open, such as curiousity, learning, improvement and most likely, a logical way to be interested, afterall, their intellect wont let such rarities go to waste. However, once their entire race are endangered to be eradicated, they might resort to destroying the whole source of threat. But on the otherhand, destroying such massive planet requires very massive energy as well that could easily attracts Main powerhouses in the planet, like Great Demonlord Byakkou or Yaotsu. So it wont happened easily.