If they want to sell more Model S, perhaps they should go check out a bottom of the line, zero options 3series/A4/CClass and see if they can bring their interior details and quality up, from below, to match those lower end cars.
Also, style and taste continue to march on ... large flat panels in your face, circa 2005, were a sign of luxury and sophistication. In 2017 it is the absence of panel displays that are a sign of luxury and sophistication.
1) They're still selling as many model S vehicles as thye can make. Perhaps the market will soften after Model 3 introduction or increase on Tesla's manufacturing capacity.
2) Any heavy add-on increases the weight of the vehicle and decreases the rated distance on a single electric charge. From their point of view it's better to let the aftermarket for interior accessories to develop, as then any add-on is at owner's discretion.
3) People who shop on interior will still go to their local Mercedes, BMW or Lexus dealer. Even other luxury brands (Infiniti, Cadillac, Acura) have had a tough time competing with decades of experience.