1. Writing for a sandbox game is exactly the same as writing for a linear narrative. It's not. It's harder because it's on a much larger scale and you don't know much about the protagonist (the player). The result is that, on average, the quality of the writing is going to be lower. That needs to be kept in mind when comparing the writing in different kinds of games. I've written in both styles so I have a pretty good idea how those conditions affect the quality of the writing.
Compare say a ME2 Companion Quest verses the civil war in Skyrim. ME2's example is well-written and strong providing meaningful choices and interesting characters. The entire Civil War quest line doesn't have significantly more writing or dialogue in it (the vast, vast majority is going to a place and killing people, very little dialogue when you think about it) and it is linear as heck. And let's be honest, ME2 companion quests really don't give a DANG about the fact you are Commander Shepherd. You could replace all "Shepherd" references with just "Commander" and make it totally generic, and it doesn't hurt the quality of the story AT ALL.
There are some types of stories that require incorporating a lot of details about the protoganist into them, but a lot of RPG stories that are strong honestly don't require this at all and they aren't that hard to write. You just make the NPCs interesting and involved and allow the player to engage in that story if he finds it interesting (which is essentially a sandbox element).
Don't get me wrong, I understand how with the dropping of AI development from Oblivion and essentially dropping Radiant Story why the average quest isn't that good in Oblivion. I'm not talking about that. I'm talking about the major LINEAR quest chains in the game. They aren't bad because the game is a sandbox. They aren't sandboxy stories at all, in fact. They're not good for other reasons.
2. That the writing is bad because the developers svck/are lazy/are greedy/are stupid/etc. Arguments that depend on speculative qualities applied to imaginary caricatures of real people are not arguments. They're emoticons. I tend not to take posts that contain irrelevant flaming seriously. Which is a shame, because there are a lot of people on these forums making good observations and then burying them under a mountain of turds.
Companies are about profit. They are about delivering a product or service that sells at minimum cost. I can't believe we're even having a disagreement over this. If people didn't buy Oblivion because they thought it had a shallow story, are you saying that Skyrim would still have a shallow story? If people didn't buy Skyrim due to the story, would the next game not fix it? Money talks, and with TES games the money says that people don't really care about good and interactive story. Or I guess you could assume they somehow aren't a business and aren't heavily influenced by the factors that influence all businesses. That seems a bit silly, imho.
The only other thing I've said on this is that I agreed with the person who pointed out the writers for Bethesda are probably rather important figures in the company. It started out a lot smaller back in the day and I believe the people who invented the lore are still around. If they have writing issues, well, corporations don't easily replace such people or their work unless there are problems selling a product. If they happen to have some mediocre writers, well, it doesn't hurt the bottom line and it would be a lot of trouble to replace them or their work, so they don't. Or do you think it is unreasonable to think Bethesda is a corporation in this manner too?
If I said they were stupid or lazy, then I take that back. I didn't mean to imply such. By the above I would only venture to say that they're PROBABLY effectively a bit apathetic about the sorts of story concerns addressed in this thread. It isn't like it would be impossible for them to do better and make a profit...but if they are still very successful, why risk anything with significant change. They're probably other factors involved in terms of company structure and the like that lend to this as well. I think it is a fairly obvious statement to say that Bethesda takes baby steps with innovations and is general very cautious in this regard. Do you disagree? I am not very surprised by this, I mean, not every company can be crazy like Nintendo.