Where do you think they would go to?Most definitely not do we want to drive all these companies away because thats what it will be essentially doing.
They want to have a presence in the EU.
American companies like the ultra-liberal model that the Brits have and that we slavishly follow.
They also like that they can do business here in English, as they are not great linguists.
Their lawyers can read our laws in the original, and propose new laws that favour them that will lose nothing in translation. We have little or no competing domestic industry which would be undermined by special deals given to US companies, so Ireland is and will remain a perfect platform for them.
There are probably other benefits to them arising from them being based here. Of course, low tax is the main one, but even without low tax, they will stay as they have sufficient muscle in terms of their very significant presence which allows them to lobby the government directly in the case of big companies and indirectly via representative organisations for those with a smaller presence.