The same thing that makes McLarens expensive. They're low-volume production, highly technological, and highly customized to the individual user. A guy who's a paraplegic might not need the kind of support that a guy who doesn't have any upper body strength at all needs. By the end, dad couldn't even lift his arm to brush his own hair. His muscles were shot, so he needed what was basically a racing seat to hold him upright. And this was a racing seat that could recline, tilt, rise up so that he could be at eye level with standing people, leg-elevate, and go completely horizontal.
You can get cheaper chairs, but... Well you can get Yugos too, y'know? The things tend to fall apart, and when you're relying on it to be your legs...
I would say things get worse because our government focuses on giving assistance to people who are underpaid rather than forcing businesses to pay people properly. Walmart is a great example. They charge very low prices. They can do this because they pay very low wages. They can do that because their employees can afford to work there because the government makes up for their low wages by giving them food/housing/etc assistance. In other words, the tax payers are subsidizing Walmart's business model. That's insane. If Walmart were forced to pay a living wage, then government charity would be unnecessary.
Anyway, that's not really about cars, but it is - because others have talked about how the poor in our country drive cars. Yes, they do, because we've set our society up such that subsistence living is very difficult to pull off if not impossible. In other words, we have to work. And because with rare exceptions our public transit system is atrocious, if we want to be able to work, we need a car in order to get to work.
It's cute and everything to point out that people in third world countries don't have cars and live in grass huts, but those people also either have a farm out back or are hunter/gatherers, or in extreme cases starve.
We need to get away from the race to the bottom mentality. Pointing at someone in a third world country and saying "our poor are better off than they are and therefore there's no problem" is not conceptually different from pointing at a $15/hour worker and saying "I don't' make that, and neither should he." The proper thing to say is "He's making $15 an hour, why the hell aren't I?" and the proper thing to say with regards to the third world poor is "yes our poor are better off than they are, and that's how it should be, and we can do even better."
Want the poor to stop owning cars? Improve public transportation so they can get to work. Otherwise, they have to have them, whether they can afford them or not. End of story.