What Seri and Kaleigh said. And I am saying this because I am myself in the graphic workflow in the industry, and I do not even want to imagine the resources needed to create massive, huge and open environnements. Either you get a FF XIII where everything, EVERYTHING is a 3D unique object, because EVERYTHING is modeled specifically for its place, and you end up with one of the most linear series, but also beautiful and NEVER repetitive. Emphasis put on the shinyness. Then you have some kind of hybrid like Deus Ex or bioware games where you are free but still with scripted parts and environnements. Or either you want something more enormous, more free with huge environnements like Elder Scrolls, GTA, etc, and you usually end up with something quite ugly, low standard or less resources demanding "per pixel" to create it. Lets face it, GTA, Red Dead Redemption, or especially the Elder Scrolls, are ugly and lot less polished compared to more linear games.
Back in the day you just basically had to crate your very low poly 3D models and add textures. Most environnements were quite barren due to technical limitations, mostly with walls and objects directly tied to gamedesign (very few things dedicated to the ambiant immersion) Now, you need concept artists, a lot of Artistic Direction skills and process, pre production, then all the creation process of 3D assets that needs : 3D models, complex animations, textures, shadering, specular, normal maps, and now even ambiant occlusion and tesseling, all this with complexe lightning and scenes full of 3D objects absolutely everywhere.
So yes, thats realism vs abstraction. It was very hard to go for full realism before, but now it is the case.
But what pisses me off these days are all the people complaining each time something is a little too linear. They are all happy to have awesome stories, universes and very well done environnements, but when the linearity comes up as a matter of fact, they all whine about it.