Of late, every time I rent a car in the US, I'm handed two copies of the key, connected by an unbreakable wire cable. This makes a big, unwieldy, lump in my pocket. It also guarantees that, if I lose one, I lose both.
Why do the rental companies do this? Naively, I would expect them to want to keep one key in a safe place in case the renter screws up and loses a key.
My recent experiences of this have been with Alamo FWIW.