Britain triggered Article 50 and decided to leave the EU. There's no deal necessary. From the EU's point of view (and a legal one), this isn't a negotiation, just a (sometimes less clearly defined) bureaucratic procedure.
There is of course the question of what Britain's relationship to the EU will look like after Brexit. And it is the EU's responsibility to negotiate a deal which makes that relationship as beneficial for EU member states as possible.
It's simply not their job to care about Britain any more.
Another point worth remembering is that several EU countries don't really have a significant trading relationship with Britain. Imagine if Britain had remained in the EU and Austria was negotiating a 'Brexit-style' deal, for example. How interested would Britain really be in whether that deal was good or bad?