While I have a one car family, most families do not. Most families have, at least, two vehicles, and many have three or more.
It make a certain amount of sense to buy one of those vehicles to meet the family's peak vehicle needs -- perhaps mom, dad, the kids, and a couple of friends, their bicycles, and their luggage on a rugged dirt path to some vacation cottage during summer vacation or Christmas Break.
But, a huge share of all of the trips made by most families are single passenger trips to and from work, single passenger day trips to business meetings and single passenger overnight business trips. On trips like these, you bring nothing but a briefcase, a lunch box and maybe an overnight bag. At peak use, you might drive your spouse to dinner, or a colleague from the office to lunch. In short, all many families need in a second vehicle is the passenger and luggage capacity of a Mazda Miata and nothing more. But, the vast majority of these trips will be made in urban traffic where a powerful engine does nothing, and people don't need their commuter car to have leather seats. An ability to park in a tight spot is more useful. The point is to keep second car costs down, not to pay the Mazda Miata price of about $26,700 MSRP.
True, there are lots of vehicles on the market which are fairly inexpensive and small, mostly targetted at single young people straight out of high school or college who needs a car, which will meet all of their needs, to drive with their friends to a party or the beach, cart all their worldly goods from apartment to apartment. The Honda Fit is the latest example of the genre and the pictures on the company webpage linked show the target audience. Another similar vehicle is the Toyota Yaris ($10,000-$13,000 MSRP, 34 mpg city, 40 mpg highway).
But, people in their thirties, forties and fifties commuting to work are a little vain. They don't want to convey the image that they are college kids, would enjoy some distinctive styling, and don't need the back seat and the gobs of potential cargo space found in most of these vehicles. They need two seats and a little bitty trunk, preferrably opaque so that no one will be tempted by the valuables you have in there.
A couple of German car companies have come close. The new VW Beetle (MSRP starting at $17,180 and up to 37 mpg city and 44 mpg highway in the diesel version), and the new Mini Cooper with BMW engineering, starting at $16,950 MSRP (27 mpg city, 35 mpg highway), are both nicely styled small vehicles, primarily designed for two passengers, although both have back seats,with only modest cargo space and decent mileage. No American and Japanese manufacturer, however, has a car in the U.S. market that is a good fit for the second commuter car role. Even the Beetle and the Mini aren't optimal, as they devote weight (which impacts fuel economy) and length (which impacts parking usefulness) to a back seat that can actually hold a couple of adults, which also contributes a little to the price of the vehicle, both in terms of materials cost and necessary engine size.
Why can't they make a two seater commuter car, with a small trunk, which is pretty inexpensive (I'm thinking under $14,000), gets good mileage (is 40 mpg city and 50 mpg highway too much to ask?), easy to park, and looks decent? It doesn't have to have a powerful engine. It doesn't have to have sports car styling. But, it does have to be something respectable.