Exports to the EU are worth 12% of the entire UK economy. Worst case scenario, tariffs on WTO terms will make a dent, but not stop it all together. Even if that full 12% stopped, it would be worth it. Other countries have sacrificed far more to be free than a mere 10% drop in income.
You’re ignoring that the UK is the locus for the entire continent’s financial services industry, an industry that creates a massive amount of wealth, taxes and jobs for the nation, and an industry that is leaving London because of Brexit. Goods exports are not really the story. Services exports are where the money is.