There is possibly an unspoken agreement between Govt / Dept of Transport and BA regarding connectivity to northern UK, N Ireland and engineering at Cardiff. Spreading the economic benefits of BA across the UK ensures no major objections by regional MPs when BA wants a favour from Govt. If BA had dropped Belfast when taking over BD, would someone high up in Govt perhaps have erected a few barriers to the takeover ? Was opening a new Leeds-Heathrow route the absolute best possible route for revenue compared to elsewhere in Europe, or was it partly to show BA as supporting Britain and remove objections from some people to a BD takeover ?
When Flybe announed they would drop LGW-INV, people with easy access to Downing Street made public their objections to reduced service on the London-Inverness route. Easyjet were very quick to announce increased service with an early morning flight out of Inverness, at which point all the political noise suddenly went quiet.
All very difficult to prove as if anything is done it'll be as a verbal gentleman's agreement, but when big business needs a favour around regulatory approvals, one should expect some sort of quid pro quo somewhere. There is a reason that Govt lobbyists exist. Michael O'Leary's mistake has been to ignore this concept and just sue instead.