I can’t prove it, but McD’s fries, burgers and shakes tasted better (to me as a kid, anyways) back in the 60’s.
It was exciting as a kid, especially in the early days of franchise food. Also the smaller menu probably lent itself to better quality. If you watch any of those restaurant rescue shows you see big menus are a constant and one of the first things the rescuer changes. A restaurant has to know who they are and stick to that, I’ve lost count of how many times McD has “introduced” salads to the menu, only to have them fail because who the heck goes to McD for a salad. But those salad failure take money, time and real estate that could be getting used to make better burgers. They could also probably due to borrow a page from Dominos and mount a “we get it, the food sucks, and now we’re going to fix it” campaign.
They did, The fries now are terrible. Had better cardboard.
I worked at Mickey D's when I was a teenager back in the 70's. The food was a lot better back then. The beef they are using now seems to be lower quality.