You still need to have motives for those you meet along the way. Especially if they are going to help the hero. Double especially if all they do is help the hero. Even in fairy tales, the "donor" character test the hero before they hand over the goods.
Doesn't actually have to be complicated. A perfectly adequate motive is that they are afraid of what will happen if the Chosen One doesn't do the job. Then, of course, you have to give them reason to know what will happen if they don't. If the portents or what have you are impressive, curiosity would do the job. But, on the other hand, helping the hero may be a good way to have an eye to the future, and if it's not, that doesn't mean the characters have to know that.
A dedicated organization doesn't answer the question. It only raises the question of why the organization was founded in the first place, and why the characters belong to it. And why the organization has not become moribund. They tend to be very, very, very old organizations. Even a religious organization has to have some reason why people find this their vocation.