I think the requirements are driven by the desire to take candidates eligible for Zero Flight Time (ZFT) training. Similarly, I imagine pilots with B744 or Airbus ratings, especially 330/340, are ahead of the pack as the company can save money on their training.
I don't doubt the flying ability of, for example, fast jet pilots, but airlines ops are all about making money. It's that simple.
FWIW Virgin already has a good mix of ex mil and civvy trained pilots.