While it’s true that Ireland continues to benefit from EU membership in many ways, the process started in the ‘60s. The government of the day offered special deals to foreign (mostly US) companies to set up in ireland. Direct Foreign Investment as it’s called here. After joining the EEC (as it was then) in 1973 that process continued. Other EU countries offer similar special arrangements to foreign companies, Luxembourg and France among them, where the tax paid by many companies is a lot lower than advertised. Basically, each member of the EU is free it’s eat it’s own tax laws in many areas. So, the 27 nations both cooperate and compete. It’s a strange system, to be fair. Also, in recent years Ireland has become a net contributor to the EU central fund, a notable change from its status over several decades. (full disclosure: I have no background in tax law, Irish or EU legislation or any other related field, but I have lived in Ireland all my 61 years and have followed most of what happens here quite closely).