As the other reply said, you don't broadcast your metal car keys to the world every time you use them.
But, also, there's a reason cars have been using microchipped keys for the last 25+ years.
There are ways to transmit information securely that prevent replay and other attacks. (See: Wi-Fi, Bluetooth, TLS, etc.) If car manufacturers weren't lazy and cheap, they could solve this problem, but they don't really care. They get money when you buy the car, then if you're car gets stolen, they get more money when you buy a replacement. Not solving the issue is in their favor.
But, also, there's a reason cars have been using microchipped keys for the last 25+ years.
There are ways to transmit information securely that prevent replay and other attacks. (See: Wi-Fi, Bluetooth, TLS, etc.) If car manufacturers weren't lazy and cheap, they could solve this problem, but they don't really care. They get money when you buy the car, then if you're car gets stolen, they get more money when you buy a replacement. Not solving the issue is in their favor.