The reason for the decline was precipitated by wanting a fully proprietary menu. They switched from selling Coke to selling HoJo Cola, among other things. That stuff was disgusting! Our family stopped going to our local Howard Johnson’s, opting for the similar Friendly’s, because of that issue.

Also, the gas crisis in the 70s greatly curtailed family travel. It suddenly became too expensive to travel long distances. (If you could even get the fuel to do so -- at one point, cars could only buy gas every other day, based on their license plate number.)