US car manufacturers were incentivized to do that and to push for policy and marketing that encourages pickup ownership because pickups have had a protective tariff, making them more profitable than other types of vehicles.

https://en.wikipedia.org/wiki/Chicken_tax

The Chicken Tax is a 25 percent tariff on light trucks (and originally on potato starch, dextrin, and brandy) imposed in 1964 by the United States under President Lyndon B. Johnson in response to tariffs placed by France and West Germany on importation of U.S. chicken.[1] The period from 1961 to 1964[2] of tensions and negotiations surrounding the issue was known as the "Chicken War", taking place at the height of Cold War politics.[3]

Eventually, the tariffs on potato starch, dextrin, and brandy were lifted,[4] but since 1964 this form of protectionism has remained in place to give US domestic automakers an advantage over imported competitors.[5] Though concern remains about its repeal,[6][7] a 2003 Cato Institute study called the tariff "a policy in search of a rationale."[4]

https://www.slashgear.com/1809287/chicken-tax-explained-history-current-impact/

If you're an automaker, you want to market those protected vehicles to consumers, because it's more-profitable. You don't really have to compete with foreign-made autos in that particular class.

And you want to lobby for policy that encourages consumers to buy them. So, for example, the US has more-stringent towing standards than does Europe. You need a bigger vehicle to tow a given amount of weight...which encourages buying pickups. And the US has emissions standards that give special preference to large vehicles.

https://newrepublic.com/article/180263/epa-tailpipe-emissions-loophole

While the new emissions rules have been praised in most coverage for tightening standards and thus speeding the transition to electric vehicles, they also preserve long-standing special treatment for big trucks and SUVs, which exempt larger cars from more stringent emissions standards. The EPA has made a little-noticed attempt in the rule to keep companies from exploiting the sorts of loopholes they have in the past, but industry giveaways that were added into the final rule could undermine their ability to reduce emissions. When the rules take effect, for instance, starting with cars in the 2027 model year, Ford Super Duty pickups will reportedly be able to emit more than three times as much carbon dioxide as light-duty pickups like the still very large Ford F-150, and nearly four times as much as a passenger car.

“The biggest pickup trucks are allowed very gentle treatment. If you create a loophole, that’s what they will drive through,” Dan Becker, director of the Center for Biological Diversity’s Safe Climate Transport campaign, says of the new rules. “Vehicles are getting larger and larger because the larger the vehicle, the weaker the standard.”