"-why is the theoretical "soul" confined to one body if it is beyond physical? And where do they come from, all of our "souls", this life energy that makes each our own?"
Well, it's a matter of perspective. Your will is your own, the focal point through which you experience the world around you and within you. There are those among us who do not see their soul confined to a physical body and do not feel themself separate from a greater whole... a matter of perspective. If you believe we are a soul occupying physical form what then do you call 'yourself'. Are you the soul or are you a physical body? are you both? and which one do you want to focus on more as defining who you are?. Most of us will only see the physical and therefore their focal point is locked on that. They will see themself as a physical being separate from everything, that's is how your 'reality' will be translated to you. The physical self is a personal expression tool, like a pencil it makes our mark. In order to interact in a physical world you require physical form. We each have our own individual form because we each have our individual expression.
Now as for why this is the case you'll need to understand the mechanics of the human psyche and how it translates a circular reality into a linear reality. And understanding the side effects of that process. Through looking at history we can also see this process at work and how it's shaped modern thinking. Through looking at the entire history of our species the path we're on will become quite clear and the answer to your question will present itself to you.
After that you can then ask the question where does the "soul" energy come from. But to do that fully you'll have to convert your thinking from linear to circular. You have to think without thought 🙂 This is what is referred to as silent knowledge.