That's true, but it's very much biased towards the rich[1]. I think what the parent is trying to say is that the only reason this issue got legal action was because the rich were the primary victims. Had it been some other public issue that doesn't disproportionately affect the rich (eg. fracking/mining contaminating ground water), there wouldn't be similar action.
If this were about shareholders, it would be a shareholders lawsuit, not an attorney general lawsuit. This is about (in theory) distorting the public market through fraud.
[1] https://finance.yahoo.com/news/the-richest-1-own-50-of-stock...