Supreme Thief's ability felt like the obvious choice in Noah's project to deepen the aspects of his laws. He wouldn't be able to use the actual stealing skill during the process, but he wouldn't need it anymore afterward since it would belong to his existence.
Moreover, Supreme Thief's ability affected only the aspects of his law, not the actual ambition. Greed, pride, and hunger were part of his true meaning, but not its foundation.
Noah would prefer to affect his ambition only after gaining a bit of experience in the process and confirming once more that everything was working well. Also, approaching Isaac's ability would be far easier after he gained access to the entirety of Supreme Thief's understanding.
