Someone, might have been Flower, once wisely observed that the EK/Cardiff thing has to do the rounds every few months on PPRUNE.....
Just think for a second about the EK route network. What they are trying to do is cover as much of the UK population as they can. Which means that they serve London (a lot), the Midlands and Wales (via BHX and MAN), Scotland (from GLA). The big hole was the North/North East, that they have now filled with the NCL service.
Why would they do Cardiff when they have great service from BHX? They may want to serve everywhere eventually, but in the meantime they will have higher priorities than Cardiff - like great chunks of Africa, Asia and North and South America.
On a different note:
At the moment the loads are around the 80 on the WW Ams
So? What's the yield? Load is pretty meanin.... oh, I can't be arsed to type it again....