They stock what will sell and in fewer models, especially at this time.
In contrast, a year ago, my local Porsche lot (Tysons, VA) had
ruby red both in base and S model, a Macadamia model (talk about rare, it even had the exterior color console), and of course plenty of black, guards red, white and silver models. No yellows in stock (my preference at the time), they said the resale value in the conservative DC area would be lower over time (I suppose that's an issue with leases which were popular at the time) and so if you really wanted yellow you had to order it. Porsche of Arlington, VA last fall had a silver 2.7 model with Carrera Red interior. If I had seen that in my early stages of looking, my brain would have probably shut itself off temporarily, and I would have snapped it up on the spot regardless of options.
I suspect some of the "one-off" vehicles which do show up may be orders which fell through (i.e., buyer couldn't get financing or got cold feet, etc).
Keep in mind you can order in any color you want for a price ($700 or so for metallic colors, $3000 or so for "special colors"), and you can pretty much go to your paint store, get a color chip in just about any shade (like those old MoPar muscle car colors like Plum Crazy), and the factory will paint the car in the color you want (for a price).