It seems like the back quiver has only disadvantages compared to a bow or side quiver. Yet many archers - including Byron Ferguson - choose to go with them.
What advantages (besides looking awesome) does a back quiver have?
A bag with a shoulder strap is super simple to dream up and create whereas a workable bow quiver is much harder to build. Of course this only matters if you are making it or don't have access to modern building methods.
You can store more arrows in a back quiver than a bow quiver. This is a matter of simple real estate. You have more space on your back to store arrows than on the side of your bow.
IMO it is a more natural and fluid motion to reach over your shoulder to grab the arrow, nock the arrow, and place it on arrow rest. My artistic skills are limited but you can picture in your mind a fluid single arc of motion. In contrast with a hip quiver where the arrows point back you need to pull back, point the arrow forward, nock the arrow, and then place it on the arrow rest. In your mind you can see that is more of an open-V motion or a big arm circle. When the hip quiver is pointing forward you need to spin the arrow (palm towards body) in your fingers or a big diagonal up and back (palm away from body) like a sword salute at a wedding after the draw before nocking the arrow. The spin can be fancy/pretty but it is easier to drop the arrow.
It seems to me that a hip quiver with the arrows pointing forward would be inconvenient because the arrows would be hitting things and generally getting in the way. Unless you're wearing a backpack arrows in a back quiver are out of the way.
Side/hip quiver pointing back:
Side/hip quiver pointing forward: