Most homes in the United States have always been painted white. Paint was first used as a preservative as much as an aesthetic expression. White was evidently believed to be more durable than other mixtrues, but there were also historical reasons for its popularity. White was associated with the classic Greek and Roman architectural forms. Furthermore, Puritans viewed color as frivolous; the “seriousness” of white continued to appeal to Americans as late a the mid-nineteenth century. . . .
In the late nineteenth century, white houses became the vogue once again, and although tastes in home colors have gone through many cycles in the past hundred years, white has never become unfashionable.
—David Feldman, from Why Do Clocks Run Clockwise? and other Imponderables, 1988.
Paint “erodes” as it ages and the filler (chalk which is white) escapes and streaks down the side of the house. If the house is white, it is less noticeable.