Compared with Michael, Vito was a big fish in a smaller pond. He limited his activities and was primarily concerned with securing what was his. His associates were long-termers. While every Mafia Don must be a controller, Vito, due to his years, position and length of association with subordinates, could afford to trust.
Michael was an over-reacher, constantly grasping for more, constantly getting deeply involved with more people in more diverse, complex and risky situations. I don't think he ever had the time, much less the inclination, to establish long-term, trusting relationships.