Well Yacht Rock is constricted to a roughly 10 year time frame between 1975-1985. It's hard to say in words exactly why but there was a certain undercurrent in our culture during that period that lended itself to carefree studio-perfect smooth music that captured a certain moment in time. A time when you could float across Narragansett Bay in a yacht with no chance whatsoever of a cell phone ringing or social media ping interrupting your perfect day on the water, sitting in a captain's chair, sockless in boat shoes, with a glass of champagne, or Lowenbrau, in your hand.
Just like nobody today can create a piece of church music that can compare to a Bach cantata, nobody today (or before 1975) can create a true Yacht Rock song.
It's just the way it is.