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.
