Given the Doctor's affinity for the British, we must assume they have disdain for the Irish and that's why they never go there.

The Tenth Doctor also falsely remembers that Gallifrey is in Ireland when he thinks he's a human in 1913 Englad

growing up there i sometimes wasn't sure ireland had a history, as if it had skipped straight from an interminable longue duree cyclical prehistory of failed uprisings to the "we don't need to talk about it" post-history of the embarrassing civil war and subsequent enforced consensus, and so may be off limits to Doctor Who for that reason. I'm sure it's explained somewhere in Faction Paradox