My guess is just physical/lazy reasons. Before this, they were homed in the UK, whose special arrangements meant that they could avoid a lot of EU regulations that way.
Then Brexit happened and they just moved to the nearest available option.
Yeah, this is pretty ahistorical; most multinational tech companies already had their EU headquarters in Ireland before Brexit. A lot of companies _did_ move operations from the UK to Ireland (or sometimes the Netherlands) as a result of Brexit, but it was mostly financial and insurance companies (plus some pharma, medical devices etc), and those didn't generally move their headquarters if they weren't already in Ireland.
Then Brexit happened and they just moved to the nearest available option.