Ireland didn't just like potatoes. In history, they completely relied on just potatoes, which was a problem because at one point, the potato crops got infected and not enough could be harvested, causing the Great Irish Famine. The Irish, having pretty much only been eating potatoes, were forced to migrate to any other country they could get into, and some of these countries (mainly the US and the British Empire) didn't like the sudden influx of Irish people, so they made laws discouraging the mass immigration.