Many Irish roads, even near very popular cities and attractions, are extremely difficult to navigate in an automobile. Very very narrow with virtually no shoulder. Accident rates, especially among renters, must be very frequent.

https://images.app.goo.gl/arKbAkKnWK1Qqi3o9

This example is far from the most difficult, it actually has a center stripe and shoulder markings. Many similar roads are tighter with no markings, and also with blind hills and curves.

If I was an insurance provider, I'd certainly try to exclude Ireland.

Oh I know, I've driven in Ireland many times. Funny thing is, the only time I've had an issue was driving late at night on an empty road. Ran into a ditch. Perhaps the traffic keeps you hyper-focused.

The trick with Ireland is to buy a policy ahead of time that covers the EU. If you neglect to do this, you will need to buy the overpriced policy at the counter.

Insurance costs in Ireland are much higher than the UK.