Why aren't cars flexible?

Another random thought strikes. . .

It's a truism that most technological innovations are preceded by nature. Computers are just very simple brains. We envied birds for flight for centuries before aircraft. Digital cameras are still light-years away from matching our own eyes. Etc. etc.

This has lead to many people looking to the natural world to try and borrow the inventions instead of coming up with them independently: People want to manufacture spiderweb silk, they're trying to work out how those odd lumps on humpback whales can give turbulence without drag, and so on.

So why is it that cars & other vehicle haven't started emulating the dolphin approach to streamlining?

Different speeds & conditions create different demands for streamlining. Dolphins deal with this simply: their surface is highly flexible, and can be 'moulded' by the pressure of water against it, almost literally 'flowing' out of the water's way and ensuring that they are always as streamlined as possible, regardless of speed or body position. I believe bird feathers do the same sort of thing in many cases, as well.

Why is this not applied to cars? The biggest concession I've seen so far is a spoiler that pops up occasionally on a few posh sports cars.

Flexible bodywork would help to improve streamlining, which obviously cuts fuel consumption. It would also be good in crashes: Cars are already designed to crumple to absorb the force of the crash, why not go the whole hog and make soft & flexible body parts? Pedestrians hit by cars would be better off, and so would all those car owners who've had a minor prang result in hundreds worth of repair bills to bend the annoying dent back into shape.

You might be able to make a case for such bodywork being less durable than the existing ones. I don't necessarily agree: There are numerous soft-yet-tough compounds already in existence, and unlike their metal counterparts, soft polymer car panels wouldn't rust.

Maybe that's the problem. I know we could produce rustproof cars right now for the same cost. The reason we don't? Nobody would replace them. Or so say the manufacturers.

Ah well. . .