Not saying it's right but the logic is that in difficult times, when a company is trying to reduce costs, LIFO might mean retraining someone on another type, which is a cost to the company, which is what they're trying to avoid.
Secondly, BA's employees are mostly from the UK, a Western European country where living costs are high and therefore salaries need to be commensurate with this. Ryanair and Wizz mostly hire cheap labour from Eastern Europe. Those airlines can therefore offer cheaper fares on the same routes. The legacy carriers have to (on some routes) compete with this. Big Europe allows these companies to take advantage of this. It is not a level playing field unfortunately, but it makes a lot of business men with friends in politics very wealthy. The US is a similar land mass size to Europe but it is one country with (broadly speaking) identical hiring and labour laws. Salaries from one state to the next are also near identical.