Not sure what you mean - one of the leads on each of the pots does eventually have to go to ground, of course. It just might be through other circuits on the way. But they all have to be in the path to ground in some way.
as an example, on the passive streamer, they are all directly grounded.
Except the tone of course, which grounds the output pin through the cap to get the low pass filter. But the others all have a terminal grounded directly in addition to the housing.
I honestly don’t know why the housings are all grounded. I mean it can’t hurt, but it’s definitely messy.