I would expect there to be several different types. Less confident or less ambitious would certainly be one, another type that comes to mind would be people who were ambitious but whose ambition wasn't furthered by being in control of the group. E.g. someone who wants to be the best in the world at X where X is any task you typically do as part of a larger team with the others doing other tasks and you just want somebody else to be in charge of coordinating the team while you can focus on X. Being a leader requires specialized skills and a lot of people might simply not have time or interest to develop those skills.