Not only that, but Ireland is only so big a market, for any product.
Many British and European retail chains have come to Ireland since the 90s as there are enough consumers with spending power to make it worthwhile.
Sadly there will only every be so many new mortgages written in Ireland. There are big fixed costs associated with mortgage provision - underwriting, a branch network,regulatory, etc. That can only be spread across so many customers. It's similar for SME lending where there are basically only three players. New Zealand - a market pretty similar to Ireland - basically has four banks of any consequence and foreign banks aren't interested in market entry as its so small.
Even if collateral could be easily secured in Ireland, I don't think mortgage lending will ever be as cheap as euro-area levels.