Population of the world in 1950 was 2.5 billion. The population of the world has over tripled. This world put a lot of scaling pressure on everything.

I didn't think plastics are used because they are considered the only submittable suitable material, but they are definitely the cheapest and easiest to use. You cannot injection mold wood to be the exact shape and size with a snug fit for something you are packaging.

The fraction of the world's population regularly consuming manufactured and packaged goods is also increasing. That increases discarded plastics and other materials.

About a decade ago I tracked down the somewhat provocative claim that contemporary New Yorkers (city, not state) produced less refuse, by mass, than those of the 1930s. My first thoughts were that total packaging weight and waste food might account for this, older packaging materials being more ecologically-friendly, but generally more massive: wood, glass, metal, etc., and refrigeration and food preservation less developed.

Good guesses, but wrong as it happens.

The culprit was coal ash, on the order of 40% of all rubbish by weight. It had been > 80% in 1900.

Building heat was supplied by boilers running on coal. That left a large quantity of fly ash as residue. As heating switched to natural gas and cogeneration steam from the 1950s through the 1960s, coal use was largely eliminated.

Former generations of New Yorkers would often refer to receptacles as ash cans, and they were traditionally made of galvanized steel, both useful when contents might contain glowing coals. As trash evolved to colder refuse, plastic bins or bags could be substituted. "[T]he New York City Sanitation Department began encouraging the use of plastic garbage bags in 1969." (<https://archive.nytimes.com/cityroom.blogs.nytimes.com/2007/...>)

Net non-coal refuse has increased, but the total, at least as of a decade ago, was still below the early-20th-century high point. Much of the current total however is plastics, and in particular disposable diapers.

I'd had additional sources on this at one point though I can't locate them presently.

This paper discusses composition and confirms the 40% & 80% figures above:

"How New York City Residents Diminished Trash", Paul E Waggoner and Jesse H. Ausubel, The Connecticut Agricultural Experiment Station, New Haven andRockefeller University, New York. October 2003.

<https://phe.rockefeller.edu/wp-content/uploads/2019/09/NYTra...>

The NYT article above also confirms "ash cans".