The UK is way richer, has roughly 12 times the population, is more powerful economically and politically, and more diverse than Ireland, and as such has more resources on hand to solve its own problems.
The Republic of Ireland has lots of parties that have some relevance on a national level. Fianna Fáil, Fine Gael, Sinn Féin, and The Labour Party are all major parties with a Fine Gael/Labour coalition currently in power. There are also smaller parties like the Socialist Party and the Green Party (which due to a coalition with FF was part of the government of Ireland in our darkest recent days) that sometimes have TDs (MPs). However, for much of the existence of the state Fianna Fáil has been running the country almost as if we were a single party state. For about 75% of the time this state has existed Fianna Fáil has been in power. They recently received a drubbing as they’re held responsible for the cronyism and incompetence that has contributed to our various fiscal woes. This last election also brought in numerous independent TDs including colourful characters like Mick Wallace and Ming Flanagan.
Proportional representation by the single transferable vote has the significant downside of promoting parish pump politicking.
From: http://www.tcd.ie/Political_Science/staff/michael_gallagher/IrishElectSys.php