It's slightly surprising that this flight hasn't worked out - Chinese tourist visits to the UK and Europe are booming at the moment, and as we know Edinburgh is a very popular tourist destination. There should have been enough demand to sustain a 2 weekly service... surely?
But as others have said, Hainan are not exactly in a great financial position, so if the route is struggling they just dont have the resources to keep it going. Anyway, lets not get too carried away - it may just be going summer only for all we know.