Sounds like you don't understand how global trade works.
The UK can very simply just walk away with a no deal Brexit. But everyone who actually cares about the British people and has more than a bit of understanding about trade cross borders understands just how insane that would be.
A no-deal Brexit would mean that all trade with EU nations would literally cease mid-transaction. Neither materials nor finished products could cross borders, money couldn't enter or leave the country. The UK is a great country with great people but it's deeply dependent on international trade to meet it's basic needs.
No matter what people wanted to believe, they can't afford a no-deal Brexit it would destroy their country's economy for decades.