Sadly, with the turbulent history of invasions, battles, and conflict of religion in Ireland's past, many of these religious structures were left to ruin in the aftermath.
People Also Ask
Irish Catholics had their churches destroyed by English power, from 1601 of the beginning from the mid seventeenth century, and riotously in the the mid-seventeenth century by Oliver Cromwell's army.
There are lots of reasons for the ruins in Ireland. Many times the stones of an abandoned structure were reused for other buildings. Some buildings (particularly cottages) were abandoned during the famine, or abandoned because no one else wanted them. Rock of Cashel is a good example.