So, objectively, late innings in close games are less exciting than early innings in lopsided games. I've had it wrong all of these years.
All kidding aside, you're clearly wrong about the excitement level and somewhat correct about the viewership. The root of that problem is the pace of the game and not extra innings themselves. After 3 slow hours, people are ready to tune out no matter what the score is. A faster paced game would retain more viewers for what everyone except you would agree is the best part.