I am not closely familiar with bankruptcy/possession law in Norway, but to understand why they would choose Ireland, you first need to investigate Norway.
Italy is a prime example, the leasing company is responsible for the bills accrued by its aircraft there so no leasing company would register aircraft in Italy just in case the airline goes bust, they would struggle getting their airframes back and they would be liable for the bills accrued by that aircraft.
So if you want the real reason why Norwegian/the leasing company chooses Ireland you need to retain yourself an accountant and a lawyer and have them write a brief for you describing the differences and advantages of each.
If you are just posting here to sh!t stir, then by all means go ahead and I will step aside.