Fast food is a field that is rather hectic, and not one person makes all the sandwiches. I don't know if you've worked at a Wendy's/BK/McDonald's/etc., but they have some of the most pain-in-the-buttocks managers, who want it in and out as fast as possible.
Also, I don't see how it is inedible. Scrape the rest off if you really don't like it and move on. At least it isn't a chicken sandwich with lettuce, tomato and no chicken (This actually happened to my father from BK)
Yea, people aren't smart, but if I had to choose between picking off a tomato, and, say, someone forgetting which pedal is the brake, I'd be happy I can still eat at all.