Too right they're angry - they have been betrayed. It's not failed because an SNP type document hasn't been produced. It's failed because the people charged with carrying out are remainers so they never believed in Brexit. They saw it as an exercise in damage limitation not an opportunity. They have failed to use the UK's strong negotiating cards, the £40 billion exit bill, the fact that the EU has a large trade surplus with the UK and also our important contribution to European security. Worst of all is Phillip Hammond's criminal refusal to plan for no-deal. How can you take part in a negotiation without being prepared to walk away?
I admit this is partly the fault of some of the Brexiteers who could have taken the reins just after the referendum (i.e. Michael Gove stabbing Boris in the back).