"Only one more chain is left, but the crystal is still very bright... I need to absorb more energy to weaken the barrier and the traps before cracking the last chain, before that I will practice this new power of mine" Liu Yang still wanted to do other things before he totally freed the old man. He would train the power of the void to get out of this place.
The sect was banished into the void and the only way out was by using the power of the void. Without that, he would be trapped inside the sect.
That's what he thought because he had the key.
The same key that can open everything could also make him get stuck in place.
The creator of the array was the same person who held the old man in place, he wouldn't let the Devourer Demon escape easily.
The person with the tattoo wouldn't come off easily either.