This is natural and a good thing: If Earth can't sustain very many people buying cars every 2 years, then we can't buy new cars every 2 years. We have to use resources more efficiently. It's a similar situation with fuel: For a long time, we built stronger engines that consumed the same amount of fuel, instead of building engines that used less fuel for more efficient use. Later that trend reversed. A similar thing happened with computers and their energy use.

I hope my kids won't have to buy more than one car in their life.

But I do agree that the middle class is in trouble in America. Today to be middle class you need at least a BS degree or equivalent skills and you have to constantly re-educate, and that bar appears to be rising steadily.