No doubt because Gil-galad had by then discovered that Sauron was busy in Eregion, but had secretly begun the making of a stronghold in Mordor. (Maybe already an Elvish name for that region, because of its volcano Orodruin and its eruptions - which were not made by Sauron but were a relic of the devastating works of Melkor in the long First Age.)
The History of Middle-earth, Vol. XII The Peoples of Middle-earth, ch. XIII: Last Writings