4 years is not a lot of time. It's somewhere in the average for today's technology. Considering how much they invested in graphics and effects in DA:I, rendering assets and cutscenes alone is going to take months.
Here's a small list of things that takes a lot of time and only multiplies as the quality rises
>High-res textures (2048, 4096)
>High-Poly models (less segmentation on models, smoother edges, so on)*
>Particle Effects (includes omni-lighting triggered by objects like gun fire)
>Shadows. One of the biggest technical hurdle game developers had to face previous generation. Shadow maps take up a tonne of rendering time and tanks framerates in games. Similar to textures, shadows have their own mapping. (games on XBOX360 and PS3 tend to use 512 or lower texture maps)
>Ambient Occlusion. Adds soft shadows and adds nice depth to everything. This nearly doubles the rendering time.
Just to give you some perspective. Pixar has two floors of it's skyscraper dedicated to rendering alone. We are talking about a floor with nothing but motherboards and CPUs to make sure they can render out scenes frame-by-frame with multiple passes to make sure they finish it in reasonable time (4-6 months). If any of them crash or the studio has some power hiccups, then all of that can potentially be lost.
Of course, a lot of this will depend on BioWare/EA. What equipment they will be using, how many render farms, how much fidelity will they aim for, how many characters in a given scene, and so on.
This isn't even including the possibility of entire segments of a game production being halt because another team has somehow screwed up or has an issue. (EG: the audio team has not finished blocking in sound effects and temp dialog for the animators).