The original forecasts were based on immediate invocation of Article 50, and without a significant intervention by the Bank of England, and without an uptick in global growth (which Britain is bottom of the class in). Instead what we got was a big devaluation in the Pound, slicing billions off the wealth of the country.

The other elements of the forecast are coming, they're just following on a time lag because they're dependent on choices getting locked in. The not so funny thing about Brexit is that it's like a game of chicken: the market doesn't believe Britain will choose drive off the cliff edge, so it hasn't priced in the damage; but that lack of pricing information makes it more likely Britain will drive off the edge.

It's one situation where markets might ironically be ill-suited to judge because of feedback effects. The worse the outcome, the less likely the market is to believe it, which sustains the delusion that it won't be bad.