It makes sense for smaller countries like mine (Croatia) because of free travel, easier access to a larger market, lower cost of doing business, and truly being too small to negotiate good terms on a global scale. It probably makes a lot less sense for UK which can negotiate it's own terms with other global powers that fit them much better.
I have no doubt there will be many negatives to Brexit, but as demonstrated by COVID situation there's a huge opportunity for UK - for example I suspect they can secure better trade deals with the US without having to worry about the protectionist interests pushed by other EU members.
The European Union has categorically failed, and if it survives this, it will need huge amounts of change.