In Emacs the point belongs to a window: this allows a buffer to be displayed in two different windows at the same time.
The mark belongs however to the buffer.
Conceptually the mark and a point determines a region. Since the mark belongs to the buffer and not the window, it is not possible to have two independent regions.
What are the benefits of associating the mark with a buffer?
Is there any discussions of this design decision (an old mailing list perhaps)?