Now why cant Winnebago make a motorhome like this - in a 25'

The reason they don't make them that short is because as soon as you buy that motor home "you always wanted", you'll be complaining about the handling characteristics.

To make one that short, you have to downsize the interior. If you're going to do that, you might as well buy a Sprinter chassis with better mileage.

Some want the large chassis in a short box so they can have the power to tow their toys, but the market just isn't big enough.