The open (Kitchen) floor plan to me represents the idea that cooking isn’t a chore separate from eating and socializing. I want to cook for an hour without being alone. Privacy in the kitchen would never be desireable. “Entertaining” doesn’t require guests. There is also a matter of space. A shared living/dining/cooking space can use a lot less space than three separate rooms. I couldn’t afford the separate solution…
But when you eliminate a wall, you eliminate a place to put bookcases and such. One of the rules in making the most of a small space is "go vertical". Walls help you do that. So that's a loss for open plans.