This is a clash of semi-overlapping, transitioning philosophies.

The global, liberal hegemony philosophy is that you can trust other countries, and countries are just economic zones with mildly different food and weather. Country dividing lines for any other purpose are bad. The UK was evil for wanting more sovereignty vs the EU; what's the difference? Open the borders. Let anyone vote. This has only recently been philosophically countered in the popular left-leaning consciousness by the war in Ukraine, where at least one border is seen to be worth defending, and in the mainstream as sovereignty and related conservative ideas are taking hold again, although with a few extra steps to make it palateable to non-conservatives.

The practical philosophy is: we already save a huge amount of money we can spend on benefits by depending on the US for defence; might as well do the same with tech. They probably know everything anyway, and what's to know? This isn't exactly countered yet philosophically, but Donald Trump is making people realise they should at least pay their own way in defense, which is helping to gradually override the prioritising of short-term vote-buying.

> The UK was evil for wanting more sovereignty vs the EU

I don't think many thought the UK was evil.

I think many thought the UK had been sold a bag of lies, and that exiting based on a very slim majority of voters on a referendum was a bad idea.