Cars, at least American cars are so large because people want them that way. Yes there are some safety laws that require at some size and weight increases. But not much. My 2019 car isn't significantly larger or heavier than my 1992. It is larger and heavier(it also has some additional creature comforts) but the differences are fairly small.
One of the issues, is the same reason crowded rooms get nosier. As cars get larger people want even larger cars, to see over and around and feel safer.
Subcompacts sold today are much larger and heavier than what they used to be. Here are the lightest cars I could find for sale in North America in 2024 in 15 minutes of searching:
Honda Fit 1,070–1,280 kg (2,359–2,822 lb)
Mazda Miata 1,058 kg (2,332 lb)
Mitsubishi Mirage 955 kg (2,106 lb)
Many of the old standbys (Scion, Fiat 500, Mini, etc) have disappeared, or gone electric (which is fine, but they're quite heavy).
Safety standards have driven a lot of that. Air bags, impact beams, high hood line for pedestrian safety, rollover protection, ABS, etc all add weight, which disproportionately impacts small cars. An SUV with a V8 doesn't care, but it's a pretty significant thing to add a few hundred pounds to what used to be a 1500 lb subcompact. It requires a bigger engine to keep performance acceptable, and now you need bigger brakes for the extra power, a better suspension for the higher center of mass, and it all just snowballs.
And that's where consumer choice comes in: people look at a "subcompact", and find that they're heavy, inefficient, and expensive, which are exactly the opposite of what they want in a subcompact car. Once you've already made those concessions, you might as well buy something bigger.
Only in that massive marketing was done to promote large vehicle classes (both minivans and SUVs) over traditional passenger cars because of loopholes in safety and efficiency laws which made them either exempt or less-constrained by them, and—while some of those laws caught up—the resulting cultural impact was sticky.
It is a combination of factors: fuel standards (CAFE), consumers favoring larger cars, SUVs being safer than sedans in frontal collisions, limited choice for smaller cars as companies stop making them due to dropping demand, and yes, safety laws in part too.
Environmental laws too. small pickups don’t exist any more because they can’t meet the MPG requirements for their body size. Giant 3/4 Tons on the other hand? Take two.
Huh? I thought it's pretty clear that it comes from light trucks having different emission standards than regular cars, which makes them more profitable for auto makers.
Cars are large today because people buy them. Bigger seems to indicate prosperity and better value. People don't passionately buy modest vehicles (except maybe cars like the fiat 500 or mini cooper)
Personally I think this has an unfortunate effect on small pickup trucks. Think of toyota's "pickup" which was renamed tacoma and then got bigger every year.