Two reasons. Firstly because the red master key holds the immobiliser code and key information for your bike. Should it get in the wrong hands a fresh key(s) can be cut from it, but not only that but can be programmed to match your ECU. Your bike can then easily be stolen with a key. Generally insurance DON'T pay out if vehicles are stolen with a key!

Secondly, you will find it impossible, should you lose a black key (or god forbid both keys), to get new ones programmed to your immobilser/ECU. This can ONLY be done with a red key. Should you lose both keys and not have the red one in your possession you're looking at having to buy a new ECU, immobiliser transmitter, tank cap, ignition barrel and seat lock just to get going again.

I find it very strange, and somewhat worrying, that a dealer supplied a bike to you knowingly without the master key!

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