When Addams placed his Family in an 1860s-style mansard-roofed mansion, he was purposely appropriating the disgust and loathing modern people felt for their grandparents' lifestyle. Such houses had become a locus of horror because they represented a Gilded Age elite whose wealth and privilege the reduced circumstances of the Depression could not match, a type of aristocratic aesthetic that modernism had reacted violently against, a world that had gone down in flames in the fires of World War I.
It is no coincidence that between the 1930s and the 1960s, Second Empire and Queen Anne houses ("Victorian" in the popular lexicon) became associated with horror not just in Addams' cartoons, but in classic films like The Uninvited and Psycho, as well as in the iconography of Halloween. Cities across the country, to "modernize," bulldozed Victorian building by the block, putting up buildings that we, removed from mid-century as far as mid-century was from the Victorians, now consider every bit as ugly as the urban renewal advocates considered the Victorian homes and businesses they razed.
Yet today when we look at the Addams Family (and here I purposely conflate the cartoons and 1960s series), a good chunk of the original bite of the old cartoons is lost because our attitudes have changed so greatly. The Addams' house would today be the envy of a gentrifying neighborhood, and who wouldn't pay thousands for their Victorian antiques--once seen as so gauche as to be worthless but now worth a fortune. Their love of exotic pets and Goth fashion is no more than that of any good hipster, and the strange foods they eat would today mark one as a gourmand, not a psycho. Even their family "witch-doctor" is commonplace today, under the name "alternative medicine" or "holistic care." Heck, the Family's beloved swamps, which in the twentieth century governments worked hard to drain, are today beloved again as "wetlands."
In sum, the strange, alien, unnerving aspects of the Addams universe are no longer the Family and their lives but the square, insular, fearful conformists who ran screaming from them.