Rowan also realized that even if the corpse of his father was not protected, it would most likely be kept inside the 9th Dimension. There was no way he could reach the 9th Dimension without the powers of a Primordial, and there was no way to become a Primordial without the eye.
This power was a quagmire that would need both incredible luck and enormous power to be able to pull off successfully.
If the Primordial Record could not show him all the mysteries behind this Will, then he may likely fall into a trap or face an obstacle that would be impossible for him to overcome due to his ignorance.
As far as he could tell his father was the only one who was killed by all the Primordials, and even Chaos was not killed but imprisoned, his power was alluring, but what if the reason he was killed was because of this power?