The Tories are at fault for never developing a Brexit plan or BSing only the positives while sweeping any negatives under the rug.
The problem with leaving an economic union is that you need to erect borders and your former free trading partners need to erect borders too.
Now all the ships and trucks that used to freely come across the channel have to go to a designated border checkpoint and every single vehicle inspected as per any border.
Additionally, standards, packaging, labelling, etc. has to change as well and now its no-longer economical to trade with the UK as you cannot use a common product (think Canadian labels vs US labels and why some products just are not available here in Canada). The logistics instantly become a nightmare and business is not worth doing.
Pre-Brexit, it was cheaper to ferry goods from Europe to the UK, drive across the land, and then ferry to Ireland. Now, despite the longer journey and cost, most routes are bypassing the UK by sea to avoid the customs red tape and to ensure the products always remain in the common market.
https://www.bbc.com/news/uk-wales-59028141