"It feels very much an anti-US rule to me."
It isn't. Quite the opposite. It's about a level playing field. There are standards for allowing products to market, some of them are more costly to implement. US car makers want to sell at lower standards than competitors, that's not a level playing field.
The customer has no right to deside on issues that affect _others_. A customer can decide on what affects the customer. If car A is more dangerous for other people than car B, then it's for somebody else than the car customer to decide what should be allowed. A car owner can't decide that "it's fine to drive this car which will kill other people because of its design".
The would be customers should decide that. If they want a car that is bigger, harder to park, has poor fuel consumption and so on.