I feel like the article lays it out pretty well? It’s a government who’s been in power too long, whose talent base was massively thinned by a Brexit Purity witch hunt and the impossibility of delivering the Brexit fairy-tale, and who weren’t simply ejected at the last election because of Corbyn’s overwhelming unpopularity.
I don't think it's a British problem either. We've had populists dominating politics in quite a few countries in recent decades. France just had a close call where a neo fascist came close to winning the elections. The Austrians have actually gone there. My home country the Netherlands has had populists come close a couple of times as well. Italy just elected a populist. The issue is that the type of policies populists preach tend to not involve a whole lot of carefully considered long term planning. Big gestures that are supposedly popular and then all hell breaks loose when reality and fantasy meet.
Brexit sounded great to people with no clue about how economies work. Now they are dealing with inflation, lots of failing policies, and the notion that they might soon have to rename their country as it is won't be great or united anymore if Scotland and Northern Ireland cease to be a part of it. I don't think anyone voted for that in England. But it would be a direct consequence of what they did vote for.