It shouldn't come as much of a surprise to people, as the resolution of textures in games increases, it takes progressively longer to develop each level. (xboxexclusive.com)
Additionally, it looks like it may even be possible to introduce higher quality textures in the game. (wccftech.com)
Developers from HexaDrive worked on the new, high resolution textures in the game. (nintendotoday.com)