The one constant in the Brexit negotiations was the EU’s united front on the message and on the strategy.
The EU also uses its unity as leverage. Getting the EU Parliament, 27 governments (and sometimes their national and regional assemblies) to agree is a tricky balancing act. A sudden shift in the EU position risks unravelling it all together. That’s why it is so hard for a third country to get the EU to move decisely away from its original position without moving substantially in return.