The other reason is that I think it devalues the brand a bit when luxury car companies release mass market versions of their vehicles. I like having something unique and would prefer not to drive yet another vehicle that you see all over the place.
The others have pretty much bashed you over the head to knock some sense into you about this so far. Just a couple more points, for my own sense of satisfaction... OK?
Tesla Motors is not, and never has been, and never will be a luxury car company.
You should read this blog post, made by Elon Musk nearly nine years ago, August 2, 2006:
The Secret Tesla Motors Master Plan (just between you and me) | Tesla Motors
Therein, Elon Musk lays down the law. The ultimate goal of Tesla Motors is to make electric cars ubiquitous, not rare... And accessible, not exclusive... And affordable, not luxurious. All while being compelling, fun to drive -- not boring, or ordinary.
Most of the traditional automobile manufacturers that have entered the North American market in the past fifty years or so have done so on the low end. Companies like Toyota, Honda, Datsun/Nissan, Hyundai, et al tried to build cars that were less expensive to buy and economical to operate. But the grand majority of automobile manufacturers over the past 120 years or so have begun on the high end instead. Cars were literally
'horseless carriages' that were considered experimental curiosities or
'toys for the rich'. There were hundreds of automobile companies prior to 1940 and they were largely custom, luxury affairs, that were built to order.
Those companies that began to offer full production, high volume, low cost vehicles used sales on the low end to support the existence of their high end division offerings. Some of these distinctions still exist in the form of Ford/Lincoln, Chevrolet/Cadillac, Honda/Acura, and Toyota/Lexus. And even within particular divisions this happens, so that the Fusion allows for the GT-40, Malibu makes the Corvette possible, and CLA-Class paying the bills for S-Class development.
It just happens that at Tesla Motors their focus is the opposite. The Model S and upcoming Model X were developed to bring about the Model ≡. So there is no need to
'protect' sales of the Generation II cars. At Tesla Motors, their Generation III offerings are the goal, not an afterthought. Though Elon would like to have a full line of cars, he wouldn't mind one bit if Model ≡ became so popular that there was no longer enough capacity at Fremont to build the Model S and Model X anymore. That would be seen as a supreme victory.