Many industries only have a handful of firms, it wouldn't be difficult for them to collude and entirely ignore a private civil society organization. Government has the power of enforcement, which is a necessary component of this goal.
Enforcing this rule is like forcing all meat manufacturers to be Kosher. As it stands those who want to eat kosher can opt to pay the extra “kosher tax” which goes to the beth din, a private organization that confirms products are kosher. Why should non Jews pays that tax. If someone would rather pay less for a product that he can’t fix, why deny him that choice.
Because it won't happen otherwise. The evidence is easily seen in the current state of these markets. If a company wanted to do this voluntarily, they already would have.
I wish humans would find these marketing tactics unethical. Instead they are manipulated by them.