Blame politics. Sounds weak, but the birth of Irish Republicanism has its origins in the rising of 1898, at a time when France (historical ally to the anti-English sentiments on the Isles, like the Jacobites) was amid a republican revolution. England was royalist, France was republican, Ireland was anti-English. The Republicanism was a product of the political situation of the time. Doesn’t make it any less retarded, but it does contextualize it.