Because, despite its box, Tarsus was an adventure module, not a board/miniatures/tabletop game like those included in FFE005. Thus, it's proper location is 'The Classic Modules' (alongside Beltstrike, Spinward Marches Campaign, et al -- all the 8.5x11 format CT product except for the Alien Modules and The Traveller Book & Adventure), which is scheduled as, IIRC, FFE009.