An occasional plot point in fiction is to have some kind of investigator buy a single share in a company to uncover what they're really up to.
If they told investors that climate change was a major threat (as they may have been legally be obliged to?) then that information would have become available to the wider public.
Also, we allow public companies to exist knowing that they will be more open and transparent than private companies. If a private company does something evil, we can knock on the owner's door. You can't do that if it's public. It's a trade-off - we don't hold an owner responsible but there's a requirement for more disclosure. If they're breaking the rules that usually stop public companies turning evil, then it's very clearly a concern.
If they told investors that climate change was a major threat (as they may have been legally be obliged to?) then that information would have become available to the wider public.
Also, we allow public companies to exist knowing that they will be more open and transparent than private companies. If a private company does something evil, we can knock on the owner's door. You can't do that if it's public. It's a trade-off - we don't hold an owner responsible but there's a requirement for more disclosure. If they're breaking the rules that usually stop public companies turning evil, then it's very clearly a concern.