That is a good point- adding an 'off' option to the coil switching would suit me very well! As Andy says, not a lot of use to normal folks though! 😄
That's even more of a personal thing, really. I've never particularly got on with passive pickup blending, and usually set my pickup heights so that the volumes are already as balanced as possible. Add to that the fact that I can be a bit of an absent minded knob twiddler on the bass, it's just easier to have switchable sounds and the one master volume. If it wasn't occasionally useful to be able to play at a reduced volume, I'd just have a master on/off, as that is mostly how I use the volume knob!