And because the distinction is what gives them value. This is the true meaning of Sithis, to break the totality of the void into meaningful shapes. So what if Auri-El's mind snapped into three pieces from his perch from eternity (Alduin/Akatosh, Lorkhan/Shor, and Magnus/Dagon)? It's better this way......
Those couples don't make sense. Alduin, Auri-El, Akatosh, Tall Papa are different visions of the same concept. These are the many names of Aka that Eat the Dreamer is referring too. They're called mirrors in Shor, son of Shor. And because this is the Aurbis, an interplay, all these gave rise to their opposing number. Shor, Lorkhan, Shezarr|Talos, Sep. Again the different visions of the same concept.
Now I'd hesitate to see purpose or meaning to the actions of half the interplay. However yes, Lorkhans actions always upset the status quo.