You can tell every consumer to check every purchase they make, and put an enormous burden on them which will not happen. Or you can legislate companies and actually get it done.
That's the point of legislation: when the free market doesn't solve something, you add rules and enforce them. That's why food products must be edible and you wouldn't ask consumers to research and pick the right ones.
> Or you can legislate companies and actually get it done.
Politicians write legislation, and are elected by the people. If the people are unwilling to sacrifice any amount of their comfort then they won't elect politicians who will make them. And let's not kid ourselves, forcing industry to be more green will come at a cost to everyone: things will be more expensive, less readily available, and possibly of lower quality.
That's the point of legislation: when the free market doesn't solve something, you add rules and enforce them. That's why food products must be edible and you wouldn't ask consumers to research and pick the right ones.