American Houses have open floor plans because it was a trend that started some years ago.
People though the homes would look nicer and be more roomy when the kitchen, living room, dining room etc were all opened up to the same spaces.
The homes do look nicer and are more spacious with the open floor plan and I loved my first house at first when I bought my new house with the open floor plan.
However after about 10 years of living in that house I decided that I really did hate the open floor concept and would prefer to have the kitchen, dining room, living room etc all separated from each other.
The next time I had a house built in a rural area and I told the builder I did not want open floor plans and wanted walls separating the rooms.
It made the house much nicer and I could keep the kitchen area away from the living room.
Most people now are actually hating the open floor concept of homes but some people still like them that way.