Lining room vs family room

Most people have a living room that they use a couple times a year, where the family room is used all the time.  Wouldn’t it be more cost effective and sustainable to combine these rooms and create one slightly larger nicer room?  The homeowner would get more use out of it and would be able to enjoy a greater space.  The downsides are that you would have to clean when someone comes over, where you could just close the door to the family room.  The other downside is that when you go to sell your home you will have one less.  However, the home would cost less and might have a higher bang for your buck.  This seems like a great thing, but then why have people not already done this.  It goes back to older times when you brought over friends and family, with the goal to impress them by taking them to your nice sitting room and having a conversation.  This has never happened at my home, does it happen elsewhere, so why still the two rooms?  We are holding on to old customs, where today we are a more relaxed culture that could probably give up a living room.  This change is starting to slowly happen through modern open concept design, where the living room, kitchen, and dinning room are combined in one larger open space.  This also allows the home to feel larger and potentially more luxurious then it would with all the separate smaller rooms.