There were guards protecting the outside, and there was no need to worry that the spirit beasts or that other people would attack. A few of them started to adopt a serious mannerism, having decided that if they did not absorb all the spirit energy here, then they would not wake up.
But just in case, they summoned out some spirit beasts. One of the reasons being, to avoid Array Masters like Sima You Lin, and another reason being to stop them from training too much, just in case they exceed the time that they have set and end up having to stay there forever.