From what is known by us about Forebearer civilization, as details of their history emerge, towards its waning days certain warlords looked to other dimensions and timelines for a desperate solution to try and extend their influence in defiance of the natural cycle. How dare they, the mighty Forerunners be faced with a decaying civilization? This could not be so!
Drochah's desperation becomes evident if you look at his tactics. According to the cyberneticized former space pirate Jonathan Judas who'd been transmogrified and integrated with a forerunner then placed in suspended animation by the dying alien, the majority of Forerunners had already banned use of Niode gates in order to purposely "time-travel" during their great War in which they wiped themselves out. Knowing your own species' extinction event is fixed and unavoidable and that at best the most you can do is shift it towards a different date to offset things, Drochah undoubtedly feels a severe drive for personal survival.
In fighting him the first time, my clan realized he was not nearly so super invincible as he made himself out to be in his propaganda (I also managed to come out of it not just alive but with an Ignis for my trouble). Perhaps the reason he had recruited thralls to act as his heralds was at least partly out of loneliness from a solitary existence. I cannot imagine what it must feel like to have been alone for thousands of years. His command mech, a towering laser powered metallic theropod in emulation of the form of a Tyrannosaurus is definitely an attention getter.
I won't pretend that I know a whole lot about how the Forerunner brain works but with the core understanding that both sapiens and pro (sp.) are part of the same genus at least some of our psychology is going to overlap.
Submitted by Mycobacter#712744