*** Also, it doesn't appear that Torrio was one to think outside the box. That's why Capone "prompted" him to retire. ***

Torrio retired because of the escalated violence and warfare with the North Siders. He was almost killed by Moran and he wanted to take his millions and live out the rest of his life with his wife without fear of being ambushed again and killed. Smart move on his part as he was one of the few gangsters to actually successfully retire (or live to a relatively long age)and enjoy the spoils of his vice empire (Lansky, Costello, Gambino).