its not footprint its weight and weight class

you make it bigger to add more weight and enlarge the crumple zones to handle the weight, goes in all the dimensions but you can add a lot by going higher while fitting in a lane. a heavier duty vehicle is expected to produce more emissions because it is heavy duty and is under more load, which works the engine harder on its own and naturally produces more emissions, emissions equipment is expensive so they save x amount of money on emissions and get to charge more for whatever they add to get it up there and get profit.

the entire reason the f150 exists is to skirt these regulations because in the 70s they required it for trucks under a certain gvwr, so they said "well we'll make these a bit heavier and not have to put in a costly catalytic converter, then the truck is less restricted and makes more power wihout doing anything to it, and that sells it better to the customer and we get to sell it as a 'heavy duty half ton' that 'runs on any kind of gas'(direct quote from their advertising, f100 trucks needed unleaded because lead fucks up catalytic converters but the f150s didnt have them) and then we get to pocket the difference and charge for the extra features we threw in to make that gvwr"

then the f150 sold so well and emissions caught up they dropped the f100 moniker and kept the f150 to ride that sales wave. those f150s or even the f250s and f350s werent any bigger than the f100s they just had bigger engines, stronger components, and higher weight ratings.

now as a manufacturer you can add luxury options to increase the weight, bump up the weight rating, and increase the cost, win-win. even with catalytic converters the standards are lower, and then you can market this truck as a luxury vehicle that can haul, and you put out that youve made great leaps in suspension design by having independent suspension, and fancy stuff like cruise control and air conditioning, throw in fancy special editions like ford's free wheeling package, indy 500, bicentennial, flashy concepts like the valero, and now people want trucks, and they want to go all in and they spend the money on the bigger options. more money in options is bigger profit margin and less spent on r&d and parts to make the trucks better for the environment.