Also after the LB everyone but the seanchan have been decimated everyone is a remnant of a remnant however I just like that phrase I'm not trying to say it can be broadly applied to others

I think that the "Remnant of a Remnant" is the Aiel having broken from the peaceful Jenn Aiel/Tinkers following the Way of the Leaf.  As Rand finds them they are already a remnant.  He breaks them with his revealing their roots of following the Way of the Leaf and saves those who can deal with the knowledge.  I just really didn't understand the Siswiamon/Spear of the dragon thing.

But why just the aiel?

Because their prophecies contain that phrase.