Most airlines do not have the own ground handling staff, they contract a handling agent like ServisAir, Aviance or Menzies. De-icing may be provided by the airport, the handling agent or a third party. I don't know what the situation was in EGGP but it may be that EZY use a different handling agent then FR or Wizz, thus they experienced problems whilst others could continue to operate. It may be that de-cing policies are different (I would hope not too different, for the sake of flight safety), or that the delays which would be result from waiting for the de-cing service caused EZY to cancel rather than incur a significant delay. Hope that helps.