Rust

Most 2000 or later cars have plastic cladding and body panels especially down low near the road. The plastic is durable and doesn't rust, so it's perfect for the application of making the car look clean and shiny for years. However, when it wraps around underneath the body, especially at the tail end of the car, it makes a shelf for salt and rust and dirt to accumulate. That rots out the steel parts of the body rapidly and is actually worse than counterproductive.

The road salt and brine solution to winter driving in snowy places just limits the life of a car to about 10 years. Also the brine runs off and pollutes streams and rivers. You would need a car lift in your garage and would need to obsessively clean the undercarriage of the car every week through the winter to keep the car in great condition for any longer than that.

It's kind of amazing there's no real solution to that problem. As far as I know, there's not even any kind of effort to solve the issue. People are oblivious to it even being a concern in their life until their car rots apart.

When I was in high school, one of my good friends had a dune buggy with a tubular steel frame and no body panels. It was a modular design vehicle. It was trivial to pull the engine from that thing or do any work on it at all because it was all exposed. It's not hard to imagine a car designed on a similar principle that would be super easy to work on, cheap, and very durable and crash worthy. The body panels could all be plastic and bolted on. The whole undercarriage could be covered with plastic panels. The entire car could be easily serviced and repaired.