The Coerthas Central Highlands are also under Ishgard control and accessible to everyone. If they could put the (very Ishgard-specific) Dragoon job quests there, they could have put the HW jobs there without breaking lore.
Some minor reworking of the jobquests would have been needed - but not all that much.
Gating the HW jobs behind access to Ishgard is a design mistake - I think almost everyone agrees on that. Luckily they at least learned and did not make the same mistake with SAM and RDM.
