"Open" floor plans have become increasingly popular over the past 75 years or so. It seems the vast majority desire it, which it why builders design homes that way. Another trend is for kitchens to become more important (and often larger) over the past century. And there once were formal areas (parlor - living room plus also formal dining room or at least area). But the trend is away from that, fewer homes have BOTH a living room and a family room, BOTH a dining room and a breakfast area. Homes are becoming more united and less formal. So, the trend is clear: toward pretty much one living area - with family room, eating area and kitchen all pretty much one open space. A LOT of modern houses are already there. It 's what most people want... so it's what builders build.
IF you view homes from before WWII (and especially earlier than 1930), you'll find "closed" floor plans - neat, individual rooms (often with doors) with important central hallways. This especially in larger homes. That's what people wanted (if they could afford it). Those days are gone.
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