Most of the FOs I have met who are leaving have all pretty much said the same thing to me anyway.
They are all very young (20s some 30s) and before they do the command, get the golden handcuffs and enjoy the left too much and can't face the thought of going back to the right and flying with those Capts that every FO knows their retirement date - they want to experience long haul.
Also all the FOs who have passed assessments for the ME carriers are being told by the recruiters tell all your Ryanair mates, get them out here and there pretty much in. They love the FR product. Used to strict SOPS, easy to train and of course tax free money.
However they have also worked out their exit strategy before they go well the smart ones have as they know even if they get a command on long haul they are not coming back to Europe to get the LHS in any established LH carrier with seniority and doing LH out of Leipzig or Liege or ACMI is not an option.
So they are keeping their noses clean while they leave as the ones I have spoken to anticipate coming back at some point as DEC 737 with Ryanair.
These are just the ones I have met.