Because when they do, they start charging more for them. cough Kia/Hyundai

Instructions unclear, now my server is slowly floating into the sky…

20 years ago:

"We need to stop using paper bags! They’re cutting down all the trees!” (a renewable resource)

"We should use plastic bags instead! They’re recyclable!” (so is paper, and it’s far more economically viable, but plastic is made from petroleum)

So now we use plastic bags made of a much heavier material, so we can reuse them, or cloth bags for a similar reason.

Cloth bags are made from cotton, like paper is made from trees.