The only excuse I needed was all ship systems could be accessed from the inside. Reduce EVA and reduce casualties.The only excuse I ever needed for a simpler looking ship is 'some designer thought it looked better'. In the late 2260s it's more fashionable to drop the Tron lighting and shiny floors and paint the walls with coloured lights. It's modern.
Tech gets more advanced and less cumbersome. More spaces needed for crew and labs over Pike's current mission.
It's all workable with imagination.