It makes sense because three is the common thread in the existance of creativity.
Earth is the third Planet from the Sun, so it is #3.
All of the following derive from 3's.
Color (3 primary colors, Yellow,Red, Blue)
Light (Actinic, Calorific and Luminiforous)
Time (Year, Month, Day) (Hour, Minute, Second)
Past, Present and Future
The Trinity (Father, Son, Holy Ghost)
Music (Based on how the third interval is played).
Mankind (Body, Soul and Spirit)
The Atom (Proton, Neutron, Electron)