why aren't the frame rails of TT set evenly from the sides?

ctying in with KMAC's thought...that COULD be....the way its designed:
front bed--dead in the middle
--kitchen, with stove and fridge...driver side
--full-size bunks...driver side
--bathroom and dinette...passenger side

this is a no-slide trailer, so THAT can't be the reason...unless maybe just maybe this design is also used on a trailer WITH a slide??? Just thinking out loud

sure wish I had a firm grip on the answer of why the frame rails are offset from center