It is obvious to me the EU see the Irish border as the achilles heel for them to focus on. The issues raised go to the heart of the future EU.
Some see it as a progression to a centrist society where the nation state is rendered redundant. Others see the future differently. No matter what terms you want to use, be it federalist, centrist, whatever,not everyone agrees. If Brexit occurs, the EU view is that the entire edifice they are aiming for may come crashing down. Where Britain goes, others will follow. The differing economies and disparities between the north and south will shortly see the euro wake up to reality. The EU made no attempt to negotiate with the UK from within the EU, now they must negotiate with us leaving. They effectively destroyed the unity themselves. Where Britain, goes others will follow and the euro will sink to oblivion. Politics cannot fight economic realities.
The european leaders will stop at nothing to bring their nightmare future to fruition, hence the continual frustration of the Brexit negotiations.