Few people immigrate to Ireland, so little point in stirring up xenophobia? My first guess at least.
PR-STV is also advantageous to vague centrists who can harvest second votes, rather than fascists who are inevitably last pick on everybody's list.
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We have quite a lot of immigrants now actually. This has made no impact discernible political impact as of yet.
But you don't have many from non-Western countries and, especially, you have few Muslims and that's generally the crucial group when it comes to mobilizing right wing populism in Europe. Islamophobia is more important than traditional racism in this context.
(its a little old, but AFAIK there hasn't been major Middle Eastern immigration to Ireland since then)