Such things do exist, but in reality are pretty compromised at being either.
You can have a vehicle that is both a car and a boat, but it will be pretty rubbish as either a car or a boat, and for much less money you could have a better car and a better boat, and a trailer so the car can tow the boat.
A car that can fly requires a pilot's licence as well as a car licence, and somewhere to take off from and somewhere to land. And again is neither a good car nor a good aircraft.
The market for all of these things is so restrictive, that there is limited development budget, and the compromises will always exist.