Saving Everyone
With the three of them working together, they had a goal in mind. To complete their plan, they needed to move on to the next step, finding the two abilities they needed: the earth ability and the water ability. The wind ability was shared with Sil as well as the acid ability.
Unlike Vorden, who could only hold one, Sil could hold many, so it was no problem for him to have both.
As the area got smaller, it would soon engulf the Chained that were located at the edge. If one of them had the ability they needed, then their plan would fail. They couldn't just sit idly by, they had to move.
There was also the possibility that the earth and water ability weren't even available as part of the Chained, but Raten highly doubted that. From what he had seen so far, all the abilities and traces of abilities around them, were ones that they had trained with during their time at the Temple, and this included the Earth and Water ability.