why do B

Because there's no such thing as a raw B&W.

The sensor in your camera shoots in Colour. Raw is a dump directly from the sensor, so you get pretty much exactly like what the sensor sees - and that's in colour

B&W features on your camera are designed to be applied to the raw data and saved as jpeg. So if you want B&W output from your camera, shoot jpeg. If you want to shoot Raw then do the conversion on your computer.

Regards

TD

Correct. Again, by definition the Raw is what you get before you apply effects.

Regards

TD