> parents with three children in car seats cannot find a sedan that can hold three car seats,
This is a categorically untrue myth. Lots of car seats are stupidly wide thrones, but there is no reason you have to buy those ridiculous things. Diono makes a full line of car seats which fit 3-across in any midsize car. They're even cheaper than a lot of seats from the biggest brands, starting under $200. [1]
People are buying SUVs because they want them and because we've made it attractive to do so:
* Externalize excess road wear costs onto all taxpayers due to gas tax
* Overall trends contributed to pathetic selection of good sedans
* Finally, Reasonable fears that since "everyone else" is driving 3-ton monstrosities, perhaps they won't be safe in a car 5 feet shorter than the truck that hits them.
It won't be easy to reverse any of this, since the only lever is to replace gas tax with a fair road tax like this Norway one -- the rest of them are functions of the trend. Sadly, anything that raises taxes on a majority of Americans (those who drive big SUV things) would be political suicide.
[1] https://store.diono.com/radian-3r/ (No affiliation with them, though I've purchased 4 of these so far personally.)