Why not?
Ask him, why not?: shepherd@archden.org
Because he's not Kerry's bishop, and has no authority unless Kerry were to present himself for communion in his diocese. Accordingly that degree of specificity would have been out of place. Moreover, it would have been counter-productive, needlessly implying that Chaput's preoccupied with the status of a certain single person, rather than the princple.
Because Kerry is not a member of his diocese.