Pierre's response about how the change in bag usage in France just happened...and that everyone thought "why didn't we do this sooner?" is a good point.
It's about something tipping the scales: we think we all know something is bad, but we never quite get around to changing it...but if we really knew, we'd do something. Sorry to link to this post again, but Ray Anderson's green conversion is a great example of how when a person's eyes are really opened, change comes...especially if that person has the power to enact the change in a real way.
We can apply pressure, raise public awareness...but inertia is a huge force. Things really do just want to stay the same.
Then there's the designer in me that says: make them cheap, beautiful and desirable and people will use them...but many projects have tried that. It's about infrastructure and top-down change, I think.