I remember when I was a very young child - more than half a century ago - getting into trouble for eating dirt. I was amused more recently to hear about my nephew doing the same thing. It seems, from my point of view, to be instinctive. I wonder why?
Family ancestors in very rural Texas used to drink “sour dirt” which was a tablespoon or two of dirt mixed with water. Intermediate generation did gather some from their favored spot and have it tested. Several essential minerals in it. Go figure.
You'd have a discontinuity. A knob naturally rotates back to its start. A slider never does and would have to pacman-wrap itself back to the start.
There's no motion you could make that would infinitely increase without a break. A knob you can just move your cursor in a clockwise circle infinitely.
There's also the issue of cargo space. The 777-300 actually has a larger hold, about 11% more. Cargo is pretty lucrative so even passenger airlines like being able to devote some of their hold space to it.
