Another lesser-known reason is sanitation. I learned this from a side job I had as a food safety inspector in the early 1980s. It's an easier job to get than most people think, and the coin wasn't bad for a part-time gig. But it very quickly turned me off from eating at restaurants -- an aversion that still lingers, by the way.
The national franchises were an exception, however. They all have high sanitation standards, and they all make surprise inspection visits to make sure the standards are being adhered to. Moreover, because the chains' standards always exceed minimum government standards, a franchisee whose restaurant fails even one state or local health inspection may very well lose his franchise. If it happens twice, then forget about it. He may as well just lock up the place and fire everyone. His franchise is history.
McDonald's standards were unquestionably the highest back then. The company was beyond fanatical about cleanliness and food safety. Their company inspectors were so anal that they must have been toilet trained at gunpoint. They'd tear half the equipment in the restaurant apart looking for a scrap of food or a drop of splashed oil. We're talking crazy obsessive.
McDonald's was in a class by itself, but the rest of the well-known national chains were also excellent. Even the brands that struck me as being least obsessive about sanitation still had higher standards than the law required, and most certainly were safe in terms of sanitation.
The other category of restaurants that had very high cleanliness standards were kosher places. I don't know if this was just a local thing, but the rav hamachshir in that locality was a certified food sanitarian in addition to being a rabbi. He must have been a pretty tough inspector because I never found a single violation in a kosher restaurant or deli in that city.
-Rich
