Not just making, but preparing. Plastic leeches into food, particularly at higher temperatures. I remember when mayo and peanut butter and so many other things came in glass jars. And pasteurization (which lets you get away with lots of unsanitary conditions) is basically heating your product while it's in the container.

Go far enough back, and you had cans of nuts with a paper insert to keep them from touching the metal.

Back then, of course, people who manufactured food understood that they were serving their neighbors, their countrymen, their people, and valued wholesomeness, making the best quality of a product they could, instead of extracting the most money they could out of slop.