Board Thread:Warhammer 40k General Discussion/@comment-24037808-20160216113913/@comment-25177957-20160217050017

1) They were "killed to a man" which means killed until the last man, which is obviously a false story, but the average follower of the Imperial Creed would not be able to decipher that, plus, it makes their tragedy sound heroic.

2)The Emperor engineered them to have weaker genetics from the start, they could not recover from grievous injuries as quick as Astartes, and thus they could fulfil two purposes, to die in battle and destroy the Emperor's foes with them. Plus, the Emperor is a master psyker, among the most powerful in the galaxy, he could have done anything to destroy them. Of course, many of the new Astartes created were also used on the remaining Thunder Warriors.

3)In "Outcast Dead" Arik Taranis captured Space Marine organs, thus their genes, and uses them to place in himself and his fellow surviving Thunder Warriors to ensure that they live longer than intended.

4)(Relates to #2)