Although Vatican fears of a possible schism of power might have some ring of tiny truth to them, the main reason for remaining cloistered at the Vatican is most likely the same as the motivating factor in his resignation.
Scandal, and a great deal of it. Once away from the protecting arms of Rome and the new Pope’s regime, just exactly how safe would Benedict be, either in his person or in a legal capacity?
The amount of attention which seems to continue to focus on the Pope Emeritus is a bit disturbing and presents an unfortunate aura of continued silence and non-action regarding rumors and accusations of abuses in the church.
If the church has any real intention of addressing these problems and repairing their deteriorating image, giving gabby reports of bi-Papal lunch dates is not the best way to go about it. This smacks of more sweeping under the rug of concerns and protecting their own.