Rather the US lax rules regarding their own enforcement.

The Double Irish (& Dutch Sandwich) where Companies routed profits through two Irish-registered subsidiaries, attributing intellectual property royalties to a management seat in a tax haven like Bermuda, is closed since 2015.

Subsequent sequential mismatch structures (the "Single Malt" tool) that replaced the Double Irish for certain firms using non-EU residency loops were also banned. Finally there's a 12.5% charge on unrealized capital gains when a company moves its assets or tax residency out of Ireland.

The headline tax rate and the effective tax rate are also very different things. France's effective corporate tax rate was actually lower than Irelands - but France is an absolutely brutal place to do business in for employers and they've comparatively no english-language tech FDI to speak of.