What incentive would an investor have to claim that a company is fraudulent if there is no financial upside to it? Altruism? That's just naive.

Sure, you could point towards regulators but we know that the advantage will always be with the regulated.

You answered it, fix regulators, and heavily punish fraud, don't let people get away with a slap on the wrist. This is literally the job of the justice system. You may as well say what benefits do police or FBI have for catching criminals. The reward is a stable and just society, on top of their salaries.

On a side note, this is one aspect that religion addresses. Ripping people off is not going to end up well when facing God.