it already on-site, have all the equipment already on-site this would add very little cost and quite profitable,
Utter rubbish. They'd have to tender at a ridiculously low price against the established handling agents who have much lower staff costs to even win the business. Having won the contract at silly / unprofitable rates, there is no way EI could make money on them with their higher cost staff.
This is not a criticism of the Aer Lingus staff, just a point about how cut throat ground handling has become.