The point of a burger is the patty. The patty is the star. Everything else is supporting cast. Otherwise it’d be called a ground beef sandwich. Lettuce adds freshness, tomatoes sweetness, onions sharpness – and crispness from all. Cheese adds umami creaminess, but the thing is, that corner’s already coverd by the meat! All cheese does – especially fancier cheeses like smoked/aged cheddar or gorgonzola – is detract from the meat’s performance.
This is only desirable if the patty is subpar. But since I only eat burger with good quality beef, I want to be able to taste the beef. Cheese, therefore, is not only redundant, it takes away from the enjoyment. Which is why I almost never order anything but the most basic variation.