I'm sure the person whose fate is to save the world from dragons would keep himself in shape. Having the option would just be gimmicky.
Why would it?
The game isn't just about the main story.
People like to roleplay,if i wanna roleplay a fat farmer,i wanna do it,where is the harm in that exactly?
Also ,it looks like attributes may have gone ( not 100% sure ),but i looks that way.
So now defining how fast or strong your PC may be could be down to the custom options to your body etc ,at the beginning.