It seems I'm rather late to the party. Nonetheless, I offer the following to the original poster:
I once asked my DnD 3.5 group if they've seen anybody else besides me take the Leadership feat or otherwise go out of their way to acquire minions/allies in other systems. Their answer was "no", and this was despite just how much help an extra set of helping hands can be, something that I proved time and again in the current campaign (do not underestimate the power of a coordinated attack, even when the character partnered with you isn't as high level as you). Heck, even a good contact can be a MASSIVE help, something that I demonstrated in my second Dark Heresy campaign where I spent 190 XP to acquire a reliable armorsmith contact (and let me tell you that that was a major sacrifice on my part as the GM only awarded on average maybe 50 XP per session). Not only was everybody able to get better armor and enjoy increased survivability in the trials that came later, our Inquisitor (yes, our boss) went and got some better armor made for himself, too, especially after suffering some debilitating injuries going toe-to-toe with a greater Slaaneshi daemon.
So what's the deal? Why do so many players seem to ignore this option even though it can make the entire group's life so much easier? Well, I think my GM's answer perhaps explains all: players (a large number of them, anyway) are only interested in personal, individual power. That is, they're only interested in abilities that will personally allow them to turn their next opponent into red paste that much more quickly. Anything else is pretty much ignored.
As for how to change that behavior? Well, one thing that I can say is that a given player group will tend to equip themselves according to the threats they keep facing. For example, in my first Dark Heresy campaign, we never bothered with trying to get meltas, bolters, or heck, even large amounts of specialist stubber ammo, and all because of the very large groups (20-50 individuals, typically) of virtually unarmored cultists we kept having to fight. Not only would the expensive ammo not have been worth it for such peons, but the small magazine capacities of the bolters and meltas (and to a lesser extent, slug-throwing guns) would have made reloading frequently a dicey proposition at best. In a Rogue Trader campaign, then, try throwing a boarding action or two or otherwise create a situation where having lots of extra friends around is more beneficial than being able to splatter a single opponent in one turn rather than two. Hopefully, when the self-aggrandising character ends up burning fate point because it was going to take 50 turns to kill that entire group of Orks all the while said Orks were shooting at him, he'll get a clue.
-Kirov, who plans on asking for counter-espionage agents-turned-wait staff the next time he gets a chance to play Rogue Trader