Why is glass too heavy? For decades, when average income was lower, it was the standard container in which soft drinks came in. Its just that plastic is cheaper, and replaced glass. But surely richer people can afford glass now.

Interestingly, both have different environmental externalities, and not sure how those have changed over the decades and will in the future.

"too heavy" is of course relative, but the addition cost/energy-use of the heavier transportation surely is non-trivial? If the bottles are to be reused, volume become an challenge.

I admit I don't have any references at hand, but I'm quite sure I've seen articles claiming plastic bottles "win" by a comfortable margin from an energy perspective.

Of course - energy is not everything.