I know nearly nothing about this field and yet at least one big reason is obvious to me: A country set up for global trade is not ready to lose access to that

I know nearly nothing about this field and yet at least one big reason is obvious to me: A country set up for global trade is not ready to lose access to that trade. They depend on things not produced locally, and depend on the proceeds of exporting things they produce in surplus. It would take decades to adapt by returning to a self-sufficient economy. And some goods (phones, for instance) could barely exist without global trade, so an embargoed country will lose access to those things inevitably.