Good question. Jacob had to physically leave the island because he paid for the lunch box childhood Kate had stolen....from a scientific point of view, one could argue that the keeper of the light was given the ability to move is both space and time at will....without having to turn the wheel like Ben and Locke had to do....   See 4 other replies

Maybe Jacob doesn't touch people to make them come to the Island.
They always were meant to come to the Island. And they had been his candidates before that, but Jacob touches them to give them a gift of his "blessing" or cast a protection spell over them that would make it so the Monster couldn't kill them directly, even after Jacob had died. When Mother was Protector of the Island, she had made "rules" or manipulated reality and made it so Jacob and his twin couldn't kill each other and Jacob also had this ability.
I think that's why there are mentions of being blessed,lucky or cursed throughout the show. Whether Jacob had met any of his candidates more than once is a mystery.
Man in black told Sawyer that Jacob had manipulated all of their lives, but he was probably lying to make Sawyer hate Jacob, too.
Destiny made them go to the Island and Jacob wasn't in control like a god, or master of their whole lives.As for leaving the Island maybe the energy field/time displacement shield was something Jacob was not effected by or something he could control.
Or maybe Jacob could only leave the island if it was in service of it.
With LOST there will always be mysteries that's part of the fun of this series (to me at least). And I don't think it's all just "bad" writing. I think they did it on purpose to leave fans' space to imagine stuff or maybe for them to make a movie one day, if we're "lucky."   See 4 other replies

This touches upon another inconsistency of the show. How does Jacob leave the island?   See 4 other replies

LOL whoever decided to have him do that was an idiot. But it's not like Jack didn't deserve it haha!   See 1 other reply