Its usage in the Amarna letters is due to the letters' topics of "hostilities", "war", or "warfare" in the discord amongst the city-states and the regional discord in the Canaan region.
A large subset of the Amarna letters are written by vassal kings in governorship of cities, towns or regions in Canaan.
The end result cuneiform sign is easily compared to a "squashed-X" alphabetic.
[1] Any syllabic cuneiform sign with 'n' or 't' can supply the beginning or end of "nukurtu".
In the Epic of Gilgamesh, the KÚR sign is only used twice and only once for nukurtu, Tablet VI, line 40: "...a battering ram (Akkadian "iašubû") that attracts the enemy-('nukurtu', "hostility", nu-KÚR-ti)[2] land,...." A partial of letters and the spelling of "nukurtu":