If I remember correctly
salad bars came into
prominence in the
mid 1970s. There's probably lots of reasons for this--the most notable being the reduced labor costs, and making the consumer feel they had
control over their
food, but still were having someone else
prepare it. I remember as a kid, though a
restaurant with a
salad bar was a
big deal.
Also, keep in mind the salad bar was invented long before the sneeze guard. Even with sneeze guards, salad bars could have other hygiene problems. You don't know where people have put the tongs, people could have handled the food, people shorter than the sneeze guard (me, for instance) could have sneezed or spat in the salad bar, improper temperatures could make food spoil, etc. Not to say there aren't well-managed salad bars out there, just that it's caveat emptor.