Because Ireland has signed treaties that restrict its actions? If they don't like the rules they can leave the EU. Sadly for them leaving the EU would also make

Because Ireland has signed treaties that restrict its actions? If they don't like the rules they can leave the EU. Sadly for them leaving the EU would also make them less interesting as a tax haven. Choices choices. Also this is not just about 'taxation policies'. They are pretty free in their policies, except that they can't make exceptions for particular companies because such special deals give a company a competitive advantage, distorting the market.