[johannes1234321]

Which office? Facebook's or the data protection agency's?

EU (more or less) has rules that the countries are primarily responsible for execution of the law and it makes sense that if a local shop causes privacy issues they should be handled by a local authority.

Now companies like Facebook play the system a bit. As first line of defense they claim that their European offices are just resellers of ads etc. and the actual operations are done by Corp U.S. (or Corp Bahamas or something) and for a second line of defense pick the country with the "best" enforcement and taxation track record. That can be done as in order for not each country trying to go after their local subsidiary the country with the European headquarters can go after that HQ for all larger cases.

Now the Irish government is smart - they see that 1% taxes on all of European business of Corp is better than 40% of only Irish business, thus they don't employ overly strict oversight.

Does it make sense for corporations like Facebook? Probably not. But for changing this this requires a unanimous change of EU law in the EU council and getting Irish to agree to that is tough, essentially meaning to pay them subsideries for their farmers or something to compensate.

Also, why to U.S. corps go there besides taxation? Language and common law. Essentially going to UK and Ireland is the easiest for U.S. lawyers to work with, as legal traditions and language are closer than on the continent ... and especially now after (formal) Brexit the choice is simpler ...