It's also the pattern of plenty of bad ideas.
How does staying in the same vehicle help? Is it really that big of a deal to move between your car and your airplane?
Let's not forget that airplanes need a preflight inspection before you fly if you're not suicidal, and having just driven the airplane to the airport doesn't eliminate that need. Quite the contrary: being exposed to the stresses of driving will increase the need for a preflight inspection.
The time-consuming non-flying activities for an airplane are preflight inspection, flight planning, clearances, etc. A roadable airplane does nothing at all to help this.
Maybe you save two or three minutes out of your half-hour preflight activities. Whoopdedo. Meanwhile, you make up more than that lost time because your dedicated airplane is a better and faster airplane than the crazy "flying car".
Sometimes you're really just better off having separate objects doing what they do best. I don't see any push for amphibious cars, for example. Everybody seems to have accepted that you're better off buying a car and a boat separately. But somehow there's an obsession with airplane/cars. I blame The Jetsons.
I could be wrong, but I'm going to need someone to give me some sort of actual advantage to one of these things before I might think I am. It doesn't save you time, it doesn't save you money, so what's the point?