Maybe the fact that they are not operating the company. They maybe have a board seat. They can use that vote to get rid of the CEO and hire a new one. That CEO can then decide to give them access to files.

CEOs of delaware corps have to do whats in the best interest of the company. It is probably not in the best interest of the company to reveal documents to a shareholder for the purpose of being successfully sued by that shareholder.

Its probably entirely impossible for a random investor to demand shit.