Why were Victorian houses seen as plausible homes for monsters?
Haunted House by Sean MacEntee (cc by)
In short, it describes the interwar period as formative for creating the idea of the Gilded Age mansion as a place of mongrel (sic) agglutination in architecture and interior design, thus impure, and a sign of the excesses of the time, anti-industrial and anti-progress. In addition, there remains the idea of the grand old family and the secrets, hidden unhappiness, and isolation which may have remained in the childhood memories of artists creating in a post-WWI era - which has its own Zeitgeist, a combination of glitter and ennui/angst, both meanings of decadence. So by the 1930s the decrepit mansion 1. was actually decrepit when seen and 2. was not appropriate in several ways by economic/socio/cultural standards.
Citations and conjecture about why the Victorian house is always where the monsters live.