Perhaps it's because they remind me of dollhouses. Tiny houses (less than 7-800 square feet) have become more popular, especially because of the potential to decrease our carbon footprint by living in one that can collect rainwater, generate solar electricity, and consume less energy and resources in general.
A slide show on houselogic.com shows several swoon-worthy examples of these diminutive dwellings. This one, sized at 650 square feet, is my favorite:
What an idyllic vacation home!