It’s not that hard to read the nutrition facts label on your food packaging.
https://www.fda.gov/food/new-nutrition-facts-label/how-under...
https://www.fda.gov/food/new-nutrition-facts-label/how-under...
It was never about sugar content, but how sweet something is.
Overly sweet things can be unpleasant to an adult palate, or one accustomed to a culture of less sweet things. In simpler times, sugar content was a somewhat reliable metric of sweetness (of course it can be balanced by acid, tannins, salt etc.), so you could select a product without needing to taste it first.
In simpler times, there were no labels to judge sugary content. The regulation in USA came in 2011. In simpler times, you bought the thing and did not cared about sugar at all. Later on, you engaged in culture war whether calories should be on labeling or whether such regulation is nanny statism.
Plus, I will go out and say that amount of people who would regularly check packages to learn how sweet it is and thus estimate taste before buying was super low. It is not a great proxy in the first place.
I still rely on it. Fruit juices touting how natural they are, but bulking out on sugar via apple or orange juice, is really common. You learn to watch out for it in various snacks for toddlers too.