Shaping the world felt wrong. In Walker's mind, he could say that he didn't want to change the way that nature flowed. It felt wrong. Even the mana felt somewhat unwilling.
However, that was just part of what he felt was wrong. He could sense that the manas around were struggling to flow in general with how much the entire area had changed right away. Especially since there had been a lot of corrupted mana that was used all at once to create a wall of bones becoming stone, raise a ruin from the water, and even corrupted monsters around here.
Beyond that, there was the simple fact that this area had been bathed in mana to force that corrupted and chaotic mana away. It had changed the growth rate and ecosystem as a whole already. Therefore, the mana was not able to settle and begin finding the flow of how it should be moving.