I’d say it’s because they’re rich and lived in a mid century modern home, which is a fairly mainstream style today. MCM style is now being used in “cookie cutter” new construction. For example, the sconce looks like something I could buy at home depot. The home has very clean lines, is unadorned, and well manicured which are hallmarks of the style.

Also, the dad is dressed in a throwback 1920s style suit and hair. This contrast of “prohibition era” fashion and MCM design makes it more difficult to date. We see a lot of design mashups in today’s world, but it was less common in past decades, so that may be adding to the illusion imo.