User blog comment:SniperGhost/Death Before Dishonor/@comment-1223903-20100611205709

They lack the spirit due to the Angel's view of them being daemons themselves and wouldn't trust them in their vehicles. Thus when the vehicles are produced in-system they make sure that none of that stuff goes into the vehicle. Yet another reason why the would Mechanicus hate them if they knew about it.

Let me see if I got this right: The main characters get split from their units and end up at a fortress that has fell to the daemons and clean it out and meet up inside.