You could say the same about 99% of the stories that hit HN about upset customers, poor support, bad interfaces, unfair license agreements, sexist language, or whatever. Why is this a big deal?
Customers are unhappy. The why is only important to the extent that it lets you figure out how to fix it. It's a mistake made over and over and over by companies dealing with unhappy customers: "Hey, this isn't that big a deal - you guys shouldn't be that upset!"
This doesn't work; you can't argue a customer out of being unhappy, and trying to do so makes it worse. The more the customer thinks that you don't understand and sympathise with his complaint, the harder it is to make them happy. (And this is just as true - if not more so - when the complaint really is ridiculous.) Bioware has a very loyal fanbase; it's an incredibly valuable asset, and they need to keep them happy, no matter how silly the complaints may be.
tl;dr: It's a big deal because Bioware thinks (probably correctly) that a critical mass of customers think it's a big deal. And that's all that matters.
You've got a software product that you promote as having feature foo.
You sell 900,000 copies at ~$60 apiece, plus DLC, plus premiums for collectors. Many of these are pre-orders.
Users discover there is no feature foo, but rather feature bar. Feature bar was not what was described – feature foo was, and was a selling point of the product. The nature of game sales leaves customers with no easy recourse, as returns are not generally permitted.
Tens of thousands of customers, feeling deceived, revolt.
Why comment so condescendingly on a subject when you don't understand what happened? Does it play to your own personal sense of delusional superiority to think people overreacted to the ending "they didn't want"? You need to grow out of that childish mentality.
What happened was that Bioware had long promised an ending that would reflect your decisions across 100 hours of gameplay. They promised relationships would be explored and closure would be brought to the series. They promised it would not be an A-choice, B-choice, C-choice cookie-cutter ending, and it was quite literally exactly that. This wasn't a product where people expected some la-dee-da happy ending, they expected the same level of care and quality writing to be carried through to end the series, and it all falls through in what is the last 30 minutes of the game (that is not an exaggeration, the game de-rails in the final segment completely).
I did play the game and I do know what happened. I also think everyone is way overblown on this. IMO there are bigger fish to fry in the world then complaining about the ending of a video game.
Picture being excited to watch Return of the Jedi and seeing how the Star Wars saga comes to a conclusion.
Instead of the Death Star being destroyed, the Imperial assault on Endor being stopped, Vader's redemption, etc., the story goes off on a wild tangent for the last 10 minutes and brings no conclusion to anything. Did the Rebels on Endor survive? Did the Death Star get destroyed? Did Luke defeat Vader and the Emperor?
Too bad. You never get to find out, and there's other non-sensical scenes with an ending on a different planet with zero relation to anything that's happened in the Star Wars universe to date.
I ask you how is this even remotely a big deal?