From the article:

One fear is that drivers are taking part in an arms race, where they see more big cars on the road and opt to buy larger cars to feel safe.

That’s my guess as well. It won’t stop spiralling without some serious intervention.

You guys are buying those massive things in the UK? With your tiny roads? That's crazy. XD

Fear. As the system collapses people are looking for the feeling of safety and invulnerability. That's the main focus of SUV and truck marketing, that is, they sell the illusion of strength. As they destroy communities and drive human society to collapse, their marketing becomes more effective.

Bear in mind that this is new car sales, which are a small proportion of all sales. The vast majority can't afford to buy new, or don't because their limited budget buys more secondhand.

So the question is "what the fuck is wrong with rich people". Plenty of scholarship out there speculating on the answer.