This is one of my favorite demos to do because it is quick and easy to do, and the results are always dramatic. No one ever fails to hear the difference. The last time I did it the guy said, "I wish you hadn’t done that!" He was really getting into the music and when the elevators came out it was a total let down.
In no particular order, dielectric is a factor. Dielectric is the insulator around the wire. This material never is perfect. Signal peaks energize the dielectric, which then bleeds this energy back into the wire over time thus smearing or blurring detail. This definitely is a factor because I have tested it by putting different materials around the cables. Carpet, wood, concrete all have different dielectric properties. Obviously moving a cable away from these the same amount of inches will have a different effect with wood than carpet than concrete, tile, etc.
Static electricity is a factor. Anyone can demonstrate this for themselves, simply get some Static Guard laundry spray and waft it over your cables. That is all it does, eliminate static charges, and this cleans up the sound. Since static charges migrate along surfaces and the floor, be it carpet or whatever is a surface, there you go.
Vibration control is definitely a factor. Not only because the floor vibrates, but try putting your hand on a speaker cable some time while playing music with good bass content. Depending on your cable type and geometry this can be pretty dramatic. Maybe not enough to feel in all cases. But if you cannot feel it that does not mean it is not happening, more likely it is but just too little to feel. My Townshend F1 for example are supposed to be sealed in something for vibration control and I can’t feel them like I could my old Synergistic CTS. Both however responded very well to vibration control.
I know it was vibration control and not anything else because my rubber band mod was used on the same Cable Elevators, so maintained the same material and the same height above the floor. When you remove all the other variables leaving only one then you know what you are hearing is due to only that one. Which is what I did. With all this stuff.
So this is not guess, not conjecture, but tested and demonstrated. Not just on me either but lots of people. Any doubters, say again, read the system comments!