Deus didn't have any ambitions or greed in becoming a Supreme Being since he wasn't that power-hungry. Even Deus was well aware of the limits of his system considering it was only created by the System God who wasn't even a Supreme Being.
And aside from that, Deus only wanted the power that could allow him to live a slow life with his girlfriend without having to worry about problems that would hinder him from living the life he wanted to have.
What's the point of becoming a Supreme Being when on his path to becoming one, he neglected to spend time with his girlfriend that if things went well, would undoubtedly become his lover?
It wasn't worth it so Deus swore to himself that he would only obtain power as a means of living the life he wanted and so that he could reunite with his lover. But if his path of obtaining power would cause him to neglect his girlfriend, he might as well stop walking such a path that would only lead him to self-destruction.
