The tract housing phenomenon in the United States began with the post-war prosperity of the 1950's. As more families moved towards urban centers, suburbs sprang up with miles and miles of identical single-family houses on tiny lots to house them. The advantage here was that tract housing was easy to build and easy to sell and cheap enough for the first-time homeowner.
Although often mocked today, tract homes are still easy to build, easy to sell and cheap enough for a first-time homeowner.