For me it's because I want an electric car and don't really care about other modes of transit. I don't want to be in a dense city, and a car is far more practical outside of one.
That house would be even cheaper if there were less demand for it, and there would be less demand for single family homes if the supply of medium density dwellings were improved. Lots of people would want to live in the cheaper to build, cheaper to live in terrace houses, row houses, duplexes, town houses, flats, and brownstones. And with people moving out of the suburbs, your suburb house would get cheaper.