Writing a future can be hard, go to far and the setting loses relevance, but go to close and the future aspects become near moot. Thus, writers often use levitation as a visual shorthand.
Perhaps borne from the idea of Flying Cars
, a Floating Future is a place were everything, cars, trains Anchors
In the Jet Sons
, things as simple as plates, and tables float.
Futurama spoofs this sci fi trope, billboards, signs, underpants etc all float.