Once established, its very difficult to move a HQ, not just your running costs, but your staff as well. Back office staff contracts will be tied to a location, unlike the crews who are no doubt expected to work anywhere. You tend to find you will have to recruit and train a whole new group of staff, as many won't want to move to the other end of the country, even with generous relocation packages, probably leaving you with large redundancy costs, plus the cost of recruiting and training a whole new group of back office staff to the point where they know your business, processes and systems.
Eastern are in a good position currently, essentially at HUY, they will be paying rent to themselves, which is keeping that money in the business, rather than paying a third party.