I don't find that lettuce, onions, or pickles cover up the flavor of the beef in a well made burger. Ketchup, which is the only condiment that I mentioned, does.
I like the flavor of well seasoned and well cooked beef. Ketchup has such a strong flavor I find that it covers that flavor up. Pretty much the same reason I don't put ketchup or steak sauce on a well made steak....I want to taste the meat. I hate ketchup on meatloaf as well