They've also got the incentive to make it unappealing as fuck for anyone else to leave the EU, because like Brits, they're going to be approaching this from a self-interested point of view rather than caring about the British public. They're fighting to keep the world's largest trade block in tact. And yes, it has become a political union (rather than the economic union that we were promised when we joined) - but they're fighting to keep Europe strong in global trade and to keep the EU stable. And considering the rise of populism in the West, I think that's understandable.
Ultimately what's best for the EU and the UK are favourable terms for both parties and for their citizens living in the UK, and ours in the EU. But there are more political considerations at play than just the economy... and those are going to make an impact on how negotiations play out.
I think that's a pretty simplistic view of things and it skips the obvious steps between where we are today and where we will be. Some of our biggest trading partners will remain major EU countries, by necessity. Whether you like it or not, they're major trade partners and our economy is tied to doing business with them. Trade talks being sorted will relieve economic uncertainty, which is good for everybody.
With the likelihood of NAFTA being renegotiated and Trump being very pro-Brexit, it would probably be in Britain's best interests to try to become members of NAFTA (despite not being... in North America). As that's the largest consumer nation in the world, a former commonwealth country, and a large manufacturing country (albeit incredibly unstable because of the aftereffects of the U.S. war on drugs). Despite Trump believing that NAFTA is a bad trade deal, if it is renegotiated it's likely that Canada and Mexico will be able to secure better trade deals than were negotiated in the 90s - and that gives us a chance to walk up to the negotiation tables to land a new and beneficial trade deal. It is likely that once we're out of the EU, NAFTA will be the largest trade block.
It won't really appeal to the nationalists and isolationists, nor does it promise to bring back manufacturing to this country (which, by the way, the real time to fight back against that was in the 1980s... rather than 30 years later after, with Western world wholly embraced globalism and convinced China to play along). But it does stand to not provide stability to British exports and our economy. But this could be the economic (not political) union that the EU was when we first joined.
Engaging in trade deals with NAFTA nations and the commonwealth is key for us going forward. The big concern then is... are we a country for sale to corporate interests. Are we going to increase privitisation of healthcare and education to be more in line with America? Are we going to remove worker protections and rights we've had under the EU to be more in line with the worker rights of the US (and as someone working in the US, I'm not sure that will be a very popular switch...) - do we have to make major changes so that we can survive in the world economy (because globalism is not going away). Can the UK economy be strong enough to prevent a major brain drain?