I'll try to finish my post soon, but basically it's a factor of the following scattered list of thoughts:

• Slot constraints, no ability to add capacity
• Feeder traffic for longhaul flights
• Highly variable number of business class travelers (many are connecting off of long haul flights)
• Different than US carriers which have as many as 10 hub cities now, whereas European carriers have a small number of hubs
• Variable pricing based on time of day (e.g. most likely to be part of a connection) when booking shorthaul, but no impact on longhaul pricing
• Tablets over laptops for some travelers
• Little competition for shorthaul business class
• Mandate that shorthaul must be profitable
• One way and no Saturday night stay business class fares
• BA annual report in 2015 talks about maximizing number of seats where slot constrained
• Vueling offers a better seat than CE, per some