User blog comment:Supahbadmarine/By Tzeentch! Here We Go!/@comment-25033299-20130211071701/@comment-3258762-20130211163343

Well, truth be told, the Astartes always did feel like a sort of back up.

It's like "Oh no, my Primarchs have disappeared! Oh well, better make some smaller versions of them...Hey, this works pretty good! Lets make thousands of them!"