It's about reducing costs for the producers and supermarkets, ignoring externalities. That is, tons of plastic that doesn't get recycled and goes to the landfill. Now the issue seems worse as another important externality are adverse effects to human health.

I can't believe costs of switching to glass or ceramic are that high. I've bought tons of inexpensive dairy and desserts that came packaged using those materials. But since most customers don't care, they tend to use plastic.