Titan pledges New Monarchy because he is loyal and believes the idea of a king can give him more purpose to his destructive nature. Warlock pledges Dead Orbit because he is obsessed with the Void and the unknown, therefore a faction dedicated to expanding civilization into unknown space is fascinating to him and gives him reason to explore unknown space. Hunter pledges Future War Cult because he was a convict before his Ghost found him and he cares about little more than personal gain and killing.