It has to do with anti collusion laws. Companies are not allowed to all agree to raise prices together, for example. And tougher pollution standards is more expensive to manufacture. So if any one company decided on their own to raise their own standards, they would be at a competitive disadvantage if everyone else was selling cheaper cars. So the only way to do this is to get everyone else to agree to the same thing. But that type of agreement is illegal, which is why companies will often lobby for tougher legal standards because everyone else would have to comply also.