I don't see any issue with stopping to fight. Spence landed bombs in the 6th. More in the 7th. More in the 8th. More in the 9th. More in the 10th. The fight was over.

Frankly having watched the fight 4 times I am even more impressed with Brook each time. Spence landed some big big punches even early in the fight. Just, Kell has a hell of a beard and a hell of a poker face. Dude fought until there was no hope. Expecting more than that is absurd. Even if the eye injury didn't happen Spence had wore him out. Add an injury and no shot at victory, no reason to fight on.