It appeals to the millennial ethos of technology and functionality
Your smartphone bundles hundreds of apps that are all accessible from a central screen. Why shouldn't your car? One look at the Model 3's interior and iPad-like dashboard screen and it's almost as if this is the car Apple wishes it had brought to market. It appeals to millennial sensibilities; that is, those who are blasé toward purpose, but obsessed with form and function.
When it comes to technology, user interface and experience are the entry points to design. As the fourth vehicle from the first truly connected car company (i.e., it offers owners over-the-air updates for key vehicle software), the minimalist Model 3 exemplifies function over form.
But what remains unclear is the real reason for the lack of features (and clutter) in the Model 3's interior. It may have had something to do with cost cutting -- it's not inexpensive to design, develop, purchase, and install batteries and motors -- and it's also telling from Musk's elusive tweets that the production-ready interior might not be anything like what we've seen so far.