system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why aren't cars protected underneath? Why aren't they enclosed in some kind of cowling or shield? Would that help to prevent damage and rust? Is there any way to enclose your car in a shield? Would it help anything?
gpt
You can add an oil coating to prevent rust which can help. The issue with a cover is if water and salt slowly get under there over time they would be hard to wash off and would end up staying and causing rust just as much as if the parts were exposed. Also, there are hot parts like the exhaust that you wouldn’t want to cover up to avoid too much heat staying in the car and possible fires. And it would make maintenance more difficult and expensive. 

Lastly it would add to the cost of the car. If you have an old car you’re probably wishing they’d done more from the factory to make it last longer. But *if you were buying a new car* would you be willing to pay more for a car that will last longer? The manufacturer only cares about selling you a new car, not how long it lasts you. Customers will demand cars that are reliable and will pay more for cars they think will last, but this has its limits.