There's sufficient fog down our way to sometimes qualify as being appropriate for using fog lights.
The issue is that it is possible, in older BMWs at least, to switch on the foglights, and forget them. There is no indication on the dash to say they are in use. And turning off the headlights/sidelights does not cancel the foglights - the next time those lights are turned on, the foglight is there waiting.
I don't think the button on the E36 lights up to say foglights are in use, for example.
Mercedes have a system where you turn a knob to switch on headlights. Once turned, you pull it out to one position to enable one set (front or rear - I don't recall which comes first) of foglights, then pull again to enable the second set. When you turn off the side/headlights, the foglights are automatically cancelled - the knob returns to it's initial 'in' position.
So simple. So effective. So not used by so many manufacturers.