The mantle's zeal is about the Unseen ones, not Saul. He may be a saint, but not a god in their eyes, and the charr invasion was long ago. The priorities shifted to rooting out every possible threat to the mantle.
Also when Saul was still around and gave his protection to the ToA, the faith in the new gods was still very young, and was merely a new hope. It may have been just a necessary act so that the people not see the mantle as something that may endanger their way of life.