They're expensive, complicated, failure-prone and proprietary. But then again, so are some high-security door locks.
Honestly it's probably just the industry wants to keep its separate businesses which adds up to more money. People sell rfid fobs separate from their high-security keys while cars combine the two. There's no reason you couldn't take the ECU out of a Lexus, wire it up to an arduino, plug it into a wall, attach a solenoid to a door lock and weld the lock cylinder of the car into a door handle. Since modern Lexus keys act as RFIDs when their batteries die it should be mostly fail proof.
Honestly it's probably just the industry wants to keep its separate businesses which adds up to more money. People sell rfid fobs separate from their high-security keys while cars combine the two. There's no reason you couldn't take the ECU out of a Lexus, wire it up to an arduino, plug it into a wall, attach a solenoid to a door lock and weld the lock cylinder of the car into a door handle. Since modern Lexus keys act as RFIDs when their batteries die it should be mostly fail proof.