I think there is growing demand for a nice secure all in ATOL protected package such as Jet2 offers. FR's reputation for cancellations (whether fair or not) is beginning to take its toll as are seemingly endless changes to the add-on costs of flying with them.
I believe a growing number are unwilling to jeopardise their hard earned week in the sun by trying to save a few bob on the flight when they and their social media contacts conclude the airline is unreliable.