You point out to me why speaking up for the minority in the north would have required unilateral action by the Dublin government, at any point since 1922.
Dublin can't say anything because the UK is/was the main trade partner by an enormous margin.
Dublin can't say anything because it has to protect its citizens living in the UK who might be targeted in any diplomatic escalation.
Dublin can't say anything because it needs to be a somewhat neutral partner to negotiate an agreement.
Dublin can't say anything to not appear overly partisan and revanchist in case the reunification ever happens.
Dublin can't say anything because it could invite unionist terrorism in the Republic.
And finally, while it can't say anything, I don't think many people in the Republic looked too closely where someone like Gerry Adams might spend his holidays while on the run from the UK