1) The original name for Sylvanian Families was: "Pleasant Friends of the Forest Epoch System Collection Animal Toy Sylvanian Families" (森のゆかいな仲間たち エポック社 システム・コレクション・アニマルトーイ・シルバニアファミリ). Why didn't it catch on?
2) It's based on 1950s Britain. (Bonus fact: the character Hello Kitty is also meant to be British.) I think this was fairly obvious, but perhaps not so much when you consider the name of the US reboot: Calico Critters.
3) In 2006, the characters in the toy line were chosen to be the mascots for the Japan's National Federation of Workers and Consumers Insurance Cooperatives. 78 million units sold that year.
By the way, did you know that the Japanese produced an anime based on the adventures of Miss Marple and Hercule Poirot? They stuck fairly closely to Christie's plotlines - except for adding a regular character in the form of plucky young sidekick Mabel West and her pet duck, Oliver.
Sit back and enjoy the seamless genre-splicing: