The impression I've been given is that EI can't hold onto to their pilots. Aer Lingus are short of pilots partly because they precipitiously got rid of some of the more expensive older hands and partly because being an Aer Lingus pilot means you are attractive to the likes of BA or anyone really. So people are leaving for pastures new.
This would apparently apply to a lot of the self funded pilots they took on recently.
It's been suggested that these cadetships are almost a panic measure to try and get some pilots who will stay the course and not bugger off once they have a few years in an Airbus and have become very marketable.
Possibly through some heavy ball and chain bonding. These new cadets will have a big debt to pay and the partial sponsorship will ensure they're bonded for a long time. Aer Lingus are trying not to be a preferred supplier of pilots for BA DEs.
Time will tell.