I think they might have updated it once during the life of X-Plane 11 after it was updated with 11's initial release, as they did again with 12's. Two reasons for this that I can think of: (a) they want the scenery that ships with the sim to match the navigation data, and they don't do major updates to the scenery very often; and (b) it presumably costs money to license the data from Navigraph for inclusion in the base sim, and those terms will be better with older cycles (so that Navigraph can sell subscriptions, obviously).