Maybe... but the demographics of people who can accept such a small car for an only-vehicle are narrow. I don't even need more passenger space than this, and I am not a normal demographic for my age. Most people my age have a crew of children to haul around, and this car won't work for that, it will barely handle a child seat at all in the rear seats, no-LATCH, and no airbag shutoff for the front passenger.
If you take into account the economic situation of people in that demographic, a lot are 18-30 year old students, or under-employed young single people, who may not be able to financially afford a new car, even if they want one. Rent, and other expenses, and other social life aspects are usually paid first, and that pushes some of those folks toward used cars, rather than more expensive, more depreciating new cars with longer loan terms, and more interest.
As the cars become used, that demographic will likely keep the used price supported, but credit isn't as easy as it once was, and income has flatlined, while costs rise... buying power isn't as high as it used to be.
The people who have money in place to spend on this sort of car right now as it comes out new, or any new car, are increasingly older, with older children, or are empty-nesters, or otherwise haven't had children, and either completely out of the demographic for this car, or if they happen to be enthusiasts, are probably buying it as a weekend toy, not an only car.
And anyone with a cargo-requiring hobby or sporting activity is probably going to look for a vehicle with more cargo capacity, which either means FRS or BRZ won't be the only car, or something else with more cargo capacity WILL be their only car.
there are demographic reasons why sports cars tend not to be mainstream high-unit sellers. They have a big image, but they aren't at the top of the sales stats compared to other vehicles, and not many garages have *only* a sports car in them.
I have a Miata myself, but if I could only have one car, it wouldn't be a Miata, despite that we love it for what it does well. It just isn't versatile enough to be an only-car for us... and I can't imagine that it would be for anyone but a student or young person with very few practical demands.