Many employers quite rightly take the view that if you leave once, you'll likely do so again and will not reemploy. It also sends out a message to other employee's to think long and hard before jumping ship, the counter point is that by having someone back into the fold they can act as positive influence over others, whilst this counter point may have been true once, the internet age and sites such as this means no one should be joining any company without knowing what there getting into, hence the shock & awe at Norwegians ham fisted handling of its winter crewing levels, an event that will likely impact it well into next year given that on top of this they are changing the agency structure.
Meanwhile Jet2 continue in the same HR haze of interviewing/sim-in/offering employment futures with no start date and Ryanair snap up the 'hold' folk that are worth having (i know of personally of 4 now) and a number of Jet2 Captains have recently been interview by Ryanair, the main complaint being roster disruption and the near impossibility of a commute home, something that FR are now actively addressing ahead of next Summer.
Given the fiasco at Norwegian i suspect the steady flow of people they have had from Ryanair will dry up and they like Jet2 will be short of Captains going into the Summer.