Degrowth

No, vehicles have gotten larger because of the same problem as most of the issues in the United States: politics!

You see automobile manufacturers have to meet an average fuel economy across their entire fleet under the CAFE (Corporate average fuel economy) act of 1975. CAFE was a good idea as it forced the auto industry into actually improving on fuel economy year after year throughout their entire fleet or be met with steep fines for ever 0.1mpg off the target.

In 2011 CAFE was changed which directly caused the auto market we have today. See in 2011 the formula on how you'd calculate your fleet's avarage MPG got changed to now factor in vehicle footprint as a variable which auto manufactures quickly caught on to mean the larger a vehicle is the smaller their entire fleet's MPG has to be.

On top of that in 2012 "medium-duty trucks" was added as their own category with a lower MPG requirement meaning if your truck or SUV fell into that category then you would have a smaller MPG target for your entire fleet.

Now put yourself into the shoes of an early 2010s auto manufacture, would you rather design small and light vehicles that require you to meet a pretty high fuel economy level across your entire product range or would you inflate the size of your vehicles and move all R&D into finding ways to get your entire fleet classified as a medium-duty truck/SUV with a smaller MPG requirement? Of course you are going to take the latter.

The changes to CAFE in the 2010s killed small vehicles as we knew it. Ensured light duty trucks stayed dead domestically built or chicken tax be dammed. Caused the explosion of crossover SUVs to flood the market. All while making vehicles more dangerous and worse for the environment.