Eorzea was the seat of the allagan Empire, and is filled with Beast tribes who summon dangerous primals. The Xaela live in a mix of Steppe and desert that seems to lack the resources needed to sustain magitech infrastructure. As long as the Xaela give a token tribute to the Empire doesn't care.

Or perhaps they are the barbarians at the gate. Perhaps the Empire pays tribute for them to stay in the steppes and all its going to take is one Ghengis or Atilla to become the scourge of Garlemand...