Simple density.

1. True science has yet to explain what the concept of gravity actually is.
2. Boats float because their density is finely balanced with a combination of the displacement they create and surface tension of the water.
3. Birds, bees, and other flying things temporarily defeat the density idea by the use of a combination of forward motion and structures that create physical lift.

The rotation thing is a separate matter that the mods here won't tolerate being discussed.