I’m seeing the word simplistic misused a lot these days.

Simplistic means something is overly simplified. In other words, home decorating shows and fashion bloggers should not describe a room or an outfit as “simplistic.”

What they mean is that a room or an outfit is simple, which means that the room or outfit is not elaborate or ornate and is instead unadorned or not complicated — a simple room, a simple design, a simple dress, etc.