Well, if you do any digging into the history of Ireland, you'll discover that the Irish were subjugated to the English for 800 years. Catholicism was outlawed so that the Church of Ireland (England) was the dominant one and when the English would leave certain sections of Ireland, the local populace would tear down English-built places and use the materials to build their own houses. If you go to the parliament building in Dublin, you'll see huge windows all bricked up, a reminder that the English use to tax the Irish for each window in a building. Lots of historical and political reasons for these ruins. And don't forget the Republic of Ireland isn't quite 100 years old yet, even though the Celtic culture is thousands of years old. As late as the 1960s the IRA blew up a significant piece of work right on O'Connell Street in front of the General Post Office, which itself still has the bullet holes from the 1916 uprising that eventually led to the new country we know today. Now, Ireland realizes these can be major tourist attractions and is attempting to preserve around the country what is left.