I think I figured it out by Ricardus Alpert

I think I have finally figured out why none of the Others have seen Jacob, except for Richard.

You'd be surprised at how simple the answer is.

It's because of his nemesis, Mr. X

Jacob doesn't seem to be too much of a trusting type, and he seems to prefer acting from behind the scenes. Supposedly, he only communicates with Richard and has him pass his instructions to the leaders through slips of paper.

IMO, X is the reason he won't really trust anyone but Richard on the island. He knows how manipulative X is, and Richard has probably proved himself to be very loyal.

After choosing the leaders, Richard's role is not only to advise them but to observe them. Only when Richard is completely convinced that they're not prune to X's manipulations, he allows them to meet Jacob.

Now, the only leader who I think proved herself to him is Eloise. She's the only one who met with Jacob, other than Ben in "The Incident."

I'm quite sure Richard knew that Widmore wasn't as committed as Eloise was, and Widmore didn't get to meet Jacob. It is my belief that Widmore was merely a place-holder, and wasn't chosen like she was.

I think Richard was proven right when Widmore eventually "Sold his soul" to Mr. X, and probably ordered The Purge. X was presumably killed and trapped in The Cabin, while Widmore was banished.

Now, it gets more complicated when it comes to Ben. I think that while Jacob did choose Ben and wanted him to lead, he also needed him to be manipulated by X.

So Jacob refused to meet with Ben in over 12 years, because he knew Ben HAD to kill him for his own counter-plan against Mr, X to work.

The reason I think X has something to do with keeping the leaders from seeing Jacob is the scene in "Follow The Leader", when he invites all of The Others to come with him. When he tells them he doesn't know why Jacob's whereabouts are a secret and no one sees him, he shoots Richard a knowing look that seemed to indicate he knew fully well why that is.