Since the 1970's really, houses have gotten bigger as well as more expensive per square foot (with bigger, fancier kitchens and, nowadays, a bathroom for every bedroom). Builders would much rather build houses like that than bungalows for the simple reason that there is more profit in them--especially considering the significantly lower marginal costs associated with going bigger and fancier, given the sunk costs (preparing the site/infrastructure) in building any kind of house.