BA have essentially surrendered the longhaul market outside of LHR and to a lesser extent LGW. It's a lot easier for other airlines working from their hub to fly longhaul into UK regional airports. Especially with the 787 and A350.

Conversely this is why you see BA operating the 787 to places like New Orleans, Pittsburgh, Cincinnati and Portland for example.

As a GLA/EDI based traveller I would be more happy with BA adding routes from London to Places like KIX and AKL than I would to see them having regional longhaul routes.