The main thing for me is that I don't want to spend 30+ years of my life flying to China. Other reasons are as stated before, Cathay having a mixed fleet makes for more avenues of exploration and learning, and the diversity of the workplace (at least for now) is attractive for someone like me who doesn't want to work in a place that is 95% Chinese. Then there are flying long haul routes, which are much less stressful and hectic than short haul.
Of course these are all personal reasons, and one person may think different from the next, but at least for me, they make the longer progression time seem a little more worth.