Trade with any country doesn't happen because governments say so (at least not in democracies). It happens because the conditions for trade are favourable. Democratic governments can restrict trade, but almost never mandate it.
Conditions for trade between UK and the rest of the EU have been very favourable for a long time, not just because of the barrier-free trading agreements but also because virtually all the close neighbours of the UK were EU members.
Leaving the EU does not make trade more favourable between the UK and other countries, it only makes it less favourable with EU countries. So there has been no direct incentive for companies to ramp up their trade outside the EU. You might argue that they should have been making an effort to at least prepare the ground for increasing trade outside the EU, but remember that it has been literally less than two months since it was certain that Brexit would actually happen. Companies rarely put a lot of effort into preparing for something which might not happen. And they don't make that effort because "it would be good for the economy", they make if it would be good for the company.
And again remember that trade outside the EU hasn't got better. Some companies may find that trade outside the EU simply isn't worth their while - they can't make a profit doing it. And some are going to look at where they produce their goods. If they have a lot of trade with the EU it may be better for them to relocate their production to the EU.