The morale among the Kinley forces wasn't good. It was natural since most of them had fought with the discarded armies instead of demons' enemies.
The casualties weren't that great but who knew how much this state could be maintained?
The Demons had a great number of Necromancers who were using the undead that had been dying on the battlefield. Since these cowards were staying in the back, things were getting difficult to deal with.
Even if Kinley's forces manage to deal severe damage, the Demons were making up the numbers somehow.
On the other hand, Kinley's forces maintained the numbers while staying near the man-made barriers and were only being attacked.
Since they didn't have much knowledge about the other side, Sean didn't push his troops into a death trap so the stalemate continued.
It was also the same for the Demons who were finding a way to break through Kinley's formation.