The Meaning of the Advent Candles

Why are there so many different themes attached to the four Advent Candles (purple and pink). A survey of websites and books on Advent surface a number of options. Does anyone know why there are so many different traditions? Is there a source that has researched this phenomenon?

Here’s just are some examples:

Promise, Light, Love, Hope

Hope, Peace, Joy, Love

Prophecy, Bethlehem, Shepherd, Angel

Hope, Preparation, Joy, Love

Prophecy, Way, Joy, Peace

Expectation,  John the Baptist, Mary, Magi

Waiting for the Shepherd, Waiting for Forgiveness, Waiting for Joy, Waiting for the Son