[thecrazyone]

Because demand for plastic bags or similar substances doesn't evaporate. You're using a different substance instead of plastic, if you ban it. Using paper implies cutting down more trees, and paper doesn't have all the awesome properties that plastic has: high tensile strength per weight, impermeable to air/moisture, lightweight, etc.

[thinkcontext]

Plastic bags are still available, they just cost a nickel now. I can't say I've noticed any more paper bags around, can't think of a store I shop at regularly where they are even available. I believe people are using reusable bags instead.