In the 70's when fast food joints would put a bunch of pre-made sandwiches under the warming lamps, they'd make everything as is. I wasn't a big fan of onions as a kids (still don't like 'em), if we went to McDonald's they'd take a regular burger off the warmer, open it, scrape off the onions and re-wrap it. Burger King burgers were made without onions, so I started eating them.
Of course, BK fries have always sucked, so at certain points of my life I was known to go to BK for a burger and then go to McD's for fries.