Because dealerships want to charge customers as much as possible for any work on the vehicle.
£200 for an electronic radio key is just daylight robbery. Then they'll also try and charge you for topping up your oil, doing a "30 point safety check" etc.
Frankly why they don't have a usb port the user can download firmware from the internet, then upload the new firmware to the engine management unit I don't know.
Hell they can sign the binaries so that ricers can't modify it