Non recourse mortgages priced as recourse would dissuade big banks from buying existing banks.
Big banks starting fresh would find out quickly that Irish people completely mis price risk, so wouldn’t value a clean balance sheet.
To get to the level of Irish banks power in Ireland, you would need to grease a lot of the current players hands, so that would be an additional upfront and recurring cost. You don’t want the central bank and the regulator to actually do their job now do you? that would erode any competive edge a new fresh player would have completely.
A new small bank may not offend as many people so would not need to grease as many hands.