Wait I don't get what you mean Steven, it's not the EU that cares where the border is, it's the UK that does. Either the border has to go between NI and ROI in which case Good Friday agreement looks a little shaky or the border goes between NI and GB which looks terrible for the UK. In reality obviously it's going between NI and ROI, so it's up to May to try to frame that as a "victory" somehow.
It was obviously going to be an issue when the idea of Brexit was first proposed, and the fact it was never addressed until this late is just further proof that the UK doesn't give a shit about NI and they're better off forming a united Ireland.