Here's a couple points.
One, I do agree there are a lot of RP problems and roles that come off as trite in EVE RP. Granted, "Im not allowed at so-and-so's dinner party!" seems kind of silly, but such trivial things can matter at the highest levels of power.
Frankly, if someone I RPed with said "I JUST DESTROYED ALDERAAN BECAUSE OF YOUR IMPUDENCE!" I would prolly mutter "tool" and stop RPing with them. But if someone could say "for your arrogance, my alliance will take such and such constellation from the Republic and give their population to Amarrian overseers" then Im a little more impressed. A lot impressed actually.
Part of the problem is that typically, RP corps and alliances are generally small. So their ability to impact in game events is limited. And claiming to destroy a planets population comes off a bit god-moddy to me, if you cant stop it.
As for why I try to play a character who still tries to act human, or at least pretend to be, it basically boils down to this for me.
An ambitious, brilliant, powerful and amoral demi-god doing everything he can to advance to immortal full-on godhood, and conquer the galaxy, while stomping on the little people who get in his way? Kinda boring and overdone for me. I've read it before, and know how it ends.
A powerful, wealthy, destructive, murderous demi-god trying desperately to hold onto some kind of home in "mortal" society and retain some shred of humanity left in him? That actually interests me a lot more, and gives me more opportunities to write and more RP arcs to follow.