Why Not Adjustable Rear Brake Cable Stops
 

On a 'cross bike. Why Not?
I have seen in-line cable adjuster (from Problem Solvers?) but why not threaded cable stops welded to frame along top tube for addition of adjustable cable stop ends like on head tube of most road frames? Todd Richards

Who knows what goes through the head of the product managers of the big companies, but if you wanted them on a custom bike, they're available.