Scotland, Wales and NI all do so as well.
Scotland esp have appeared in several World Cups (1954, 1958, 1974, 1978, 1982, 1986, 1990, 1998). Wales in 1958, NI in 1958, 1982 and 1986.
And every WC, all four nations are part of the qualifying rounds.
I understand that they all do; I’m just puzzled by it. Unlike the Republic of Ireland, they are not countries, but states within a larger country.
(Irish people are proud of their republic, and waiting for the demographic bomb that unites them)