I think it's a fair statement that we all "RP Gallente" to an extent. As has been pointed out, the Federation is just an overly-liberal version of the Western World, which is where the vast majority of us live.
Perfect example? Me. Sure, Jakiin believes in the whole "Slavery as a path to God" thing, but interprets the scriptures with a very liberal bent (Though "Liberal Amarr" is around "Bush family calls fascist" territory, of course) and tends to believe things that they simply don't call for. Like diplomacy. And rank based on skill rather than birth (To an extent). And that ex-slaves should be treated equally to True Amarr. Etc.
This comes a lot from the fact I live in Canada. You know, the most left wing country that didn't spawn Vikings. So naturally when I'm playing my character I'm going to be pulling him to the left. This is, actually, probably true to an extent of most Amarr RPers, but that's an old argument that most here have heard and one I'm honestly a little on the other side of.
Interestingly, Minmatar roleplay is almost always the aversion of this: They avoid the republic with parliamentary democracy and all that, instead going straight for the revolutionary-esque freedom fighter line. Then again since Minmatar seem to mostly be played by rebels-at-heart, it makes sense that they'd be the ones to decide they don't need to support 'the man' to accomplish their goals.
Where was I? Oh yes.
Basically it does come down to this:
I believe this be the symptom of the general practice of roleplayers where the player pretends to be the character, therefore bringing themselves (the player) into the shoes of the character, enhancing the immersion but also bringing in all the baggage that the player has.
While there are some roleplayers that do not engage in such practices, where they actually try to keep the player as far away from the equation as possible, keeping the character at the wheel instead of having the player in the characters shoes.
I'm very much in the camp of the former, so I will necessarily be less inclined to play a character that's completely foreign to me.
But I have the sneaking suspicion that isn't the point of this topic. If it's just an issue of "Why are all the bars and scenery considered western" it's simple: That's
work. It's not even fun work like writing a good story, or slowly positioning your organization as a police force in a primarily low-security region so that you can take 'favours' from the industrialists happy to access the minerals of lowsec with relative safety and build up an empire run on equal parts idealism and naked, unapologetic greed.
Trust me, that's way more interesting than convincing people to sit on cushions and like it.