Heya,
You'd probably get a little better explanations and activity in the Sound Science forum.
What you're referring to compared to a speaker system has to do with physical location of drivers, direction of the sound waves/pressure, and the location of your two ears relative to source. Headphones don't have the luxury of being far enough away to generate a high level of separation with a degree of crossover, so that it blends. Some have tried to mimic the effects, by angling the headphone drivers, using deeper cups to increase distance to drivers, etc. But it really is a physical limitation.
Very best,