It is a good question. Why do you think it is? It is quite common to see an over-the-top modern design of a car parked in front of a colonial (or pseudo Spanish in the West) house.
Of course, people also buy those retro-looking PT Cruisers, and restore Bel Airs. Nor do only houses try to look vintage -- taste in art is also often traditionalist, and even more so in furniture.
My guess is that no one is foregoing electricity or modern pluming in order to live in a colonial. In houses, you CAN get a traditional look with modern amenities. In cars, you cannot. Imagine that Toyota built one of those royal carriage-looking limousines from the 40's, yet made them as reliable and fuel efficient as the Prius. We might yet see that; we are simply not used to the idea that cars that are not a constant source of frustration are now commonplace. Once we begin to trust the mechanics, we may turn to tradition in looks. In short, people like modern design in areas where there is a rapid engineering progress being made: they associate last year's design with poor quality, and modern looks reassure that the engineering is better. Once the technology is mature, they turn to esthetics for beauty's sake, and become traditionalists.
Good thoughts. I don’t know the answer. BTW, my wife drives a PT Cruiser!