There are "gates" at which particular goods start being requested by the Pops. So so as an illustrative example(not actual, in-game numbers), a pop of SoL 20 will not request any cars, a pop of Sol 30 will request some, and then with each sol level requiring progressively more.
This goes for pretty much all needs in the game.
As for ceilings caused by shortages, theoretically there is no ceiling if you manage to give the pops jobs that pay so well that they are able to satisfy all their needs even at +75% price of the goods.
In practice, it's all about how much your pops make, and how much of it they have to spend on their needs.