I'd disagree that people don't want deep and involving stories; I think they might want them, but they don't expect them from videogames.
Games, in general, are about getting away from reality; when one plays a game, there is an element of fantasy involved. Games enable what is impossible in the real world, such as defending the galaxy from ancient unknowable evils.
While it might not be the most original or engaging or complex story, the "hero saves the world" story is one that apparently works for games. I remember being the hero saving the world with my band of plucky companions in The Final Fantasy Legend for the GameBoy. That game was released in 1990, and Square has been pretty much remaking it since then, and the games still sell.
It may be an unfair comparison because it's a JRPG (referring here to the entire Final Fantasy series), but I think the "hero saves the world" model shows up pretty consistently in Western RPGs as well. In Diablo, you literally fight the devil. And again in Diablo II. And presumably once more in Diablo III.
Let me qualify the above by saying that I long ago grew tired of the "hero saves the day" story. After a while it just gets predictable and boring, which is precisely the opposite of what I want in a game.
There are ways to work with the formula though, and I will present as an example Bastion.
Here, the world has already been destroyed. If there were a prequel to Bastion about plucky heroes trying to save the world, then they would all die. And the world would end. Bastion certainly features a hero, doing something that resembles saving a world. "Saving" isn't the word I would use though; "salvaging" is a better fit. Bastion also scores points for its choice system, or, more accurately, lack thereof. There are, if I recall correctly, only two major choices during the game ("battering ram or Zulf?" and the ending choice, for those who have played it). Both of those choices had very significant and relevant effects on the story; carrying Zulf down that corridor, with no option but to endure the arrows and bullets of the Ura and keep going, and to see how their view of the protagonist changed as a result, is and most likely will remain one of the most emotionally powerful sequences I've seen in a game. I nearly shed a tear. Moreover, Bastion doesn't attempt to shoehorn their options into "right" or "wrong." There is definitely the choice of vengeance or mercy in Zulf's case, but either choice would make sense, and one is not morally superior to the other (you may argue that mercy is the "right" or "good" option, and that may be true, but the game doesn't present it as such). Perhaps it's merely that Bastion's choices aren't as diametrically opposed as BioWare's tend to be (more on this later); your choices are merely "Take Zulf" and "Leave Zulf" as opposed to "Take Zulf, reunite him with his long-lost family, give them 10 gold and a ticket to the land of rainbows and happiness" and "Leave Zulf, take all his money, tell his family he's a psychotic mass-murderer and then curbstomp his favorite innocent adorable puppy with a golf shoe."
And this leads me to one of my bigger gripes with BioWare: morality
I don't want games to tell me what is right or wrong. This goes into personal philosophy a bit, but I tend to take a relativist (not to be confused with relativistic! *obligatory physics joke*) viewpoint when it comes to ethics; I think people should determine what is right and wrong for themselves (PLEASE PLEASE PLEASE do not turn this into a debate on ethics. That is not my intention, and this is not the venue). I think Yahtzee does a good job of summing up my criticisms of "morality" in games in his Infamous 2 review, and I would direct you there if you are curious.
What BioWare did that I did like was the companion approval system in Dragon Age: Origins and
Dragon Age II. People have differing opinions, and I like that they attempted to bring that across in gameplay. I wish it were a little more in-depth though, such as characters having opinions on more than one topic (the example that comes to mind is Dragon Age II's "ANDERS LOVE MAGES vs. FENRIS HATE MAGES"). I believe BioWare does a pretty good job with their characters though; they make them fairly likeable, and attempt to make them relatable by giving them flaws and conflicts. They aren't perfect though, often only developing only one or two traits about a character, or basing characters on stereotypes or archetypes.
That said, BioWare characters are still some of my favorite game characters ever. Mordin, from Mass Effect 2, jumps immediately to mind (I admit I may be biased, as I myself am a man of science and was able to relate to Mordin. I never infected an entire species with infertility though.) Mordin is a complex character; he is aware of the devastation of the Krogan as a result of the genophage, and yet he staunchly defends it as the best option. He is clearly troubled by his actions though, as he has since dedicated his life to helping others, revealing a hidden guilt beneath his clinical detachment. He also has undergoes actual emotional growth when confronted by Maelon (during the course of the entire mission), which I will not spoil, but which I will say I found touching.
Personally, I would like to see a BioWare game focused on the characters themselves. Clarification: I would like to see a BioWare game wherein the characters drive the story, rather than just being along for the ride, as they seem to be in the Dragon Age and Mass Effect stories. Unfortunately, such a game would probably sell abysmally, and as such will probably never be made. Game companies still need to make money, which means they're going to stick with what sells, which means stories, in general, won't stray too far from the "hero saves the world" model (limiting ourselves to the RPG genre, remember). I commend BioWare for breaking up the model with interesting bits with their character arcs and witty dialogue, but I shake my head and tut-tut disapprovingly at their insistence of shoving 10+ hours of largely-irrelevant side quests in. I could run through Mass Effect in about 8-10 hours if I only did the main story missions, and as far as the story went, it wouldn't make much of a difference. If you're going to give me optional quests BioWare, please give me a reason to do them besides building my stats. I found myself asking why a Grey Warden tasked with stopping the ancient unknowable Cthulhu Archdemon (if we have the "hero saves the world model," we might as well run with it) would take time to run errands for people who post things on Chanter's Boards.
This post has gotten quite a bit longer than I intended. Oops. Sorry for that brick of text.
Summary: BioWare's main storylines are rather plain and unimaginative, but they add things to give the overall game variety and charm, most notably for me the characters. I wish they would focus on adding quality content instead of quantity of content, but then they couldn't advertise that the game "contains 30+ hours of gameplay!"
Just my two cents.
Please tell me how wrong and stupid I am and how I'm a total n00b BioWare fanboy.