This is an interesting take; the alternative way of putting it would be "Why are BA being honest about how long they actually think the journey will take?" Time of arrival is when they open the aircraft doors, if BA say the flight will arrive at 1300 hrs (for example), and they open the aircraft doors at 1300 hrs, does it really matter that they closed the aircraft doors (time of departure) 10 minutes, 20 minutes, even 30 minutes later than they said they would? (Granted, closing the doors 30 minutes late and still making an on-time arrival would be fairly unlikely on a short hop, but not necessarily impossible). Trains in the UK are notorious for almost always running late, one of the main reasons for that is that there is not enough time built into the timetables for boarding and alighting at stations in busy periods, I would rather the timetables were honest and a train sat at a platform for a couple of extra minutes each time than they said I would arrive at my destination 30 minutes earlier than I actually do and I wouldn't see it as an attempt to avoid Delay Repay compensation, just as a TOC actually being honest about when I would likely get to my destination such that I can choose the most appropriate train to take.