The thing is, in my opinion, the Imperials and Stormcloaks appeal to players for different reasons. I started playing the Elder Scrolls with Morrowind, joined up with the Legion then so it had a soft spot in my nostalgic mind. Of course, even then, you didn't have to play as a "loyal citizen of the Empire", but I don't recall any overtly anti-Imperial factions then (need to check this on UESP, it's been a while). Some favor the guardians of the old order who represent a continuation of the long gone Septim Dynasty (and older Elder Scrolls games to an extent) and join with the Imperial Legion or at least roleplay a pro-Imperial character. Others might find the Stormcloak story to be more appealing, the classic "rebels against the empire" scenario where an oppressed people rise up against foreign powers over them. This might be biased, but there might be proof that even Bethesda is more Imperially inclined. If this has been discussed before, I apologize, but I'd like to point out what I've seen and what I think. First off, Windhelm and the Stormcloaks are xenophobic. See what happens when you first visit Windhelm. Ask the cart driver and he'll tell you how poorly non-humans are treated. Inside, you'll see native Windhelm Nords threatening a Dunmer woman. And even if you decide to join the Stormcloaks, if you're playing a non-Nord, you'll be asked why you want to fight for Skyrim instead of being given a pat on the back. This all goes against what the old Septim Dynasty and indeed the current Empire which is cosmopolitan and an equal opportunity employer, I haven't found any orc or beast race legionnaires, but if I recall correctly, there's an Altmer(!) legionnaire commander at one of the Imperial camps south of the Throat of the World (unless this is randomly generated). If you talk to him, he'll even explain that not all elves are pro-Thalmor. Meanwhile, I've yet to see a non-Nord stormcloak. My final point is that Ulfric was clearly labeled as an "asset" by the Thalmor if you steal a dossier on him in the Thalmor embassy. An asset which has aided the Thalmor cause to disrupt order and Imperial rule in Skyrim. With such obvious clues, it wouldn't be surprising in the next Elder Scrolls game that an Imperial victory would be canon. Hopefully in the next game, we get to see Imperial vs Thalmor battles!
