Ok, so, honest question, why not? If you're correct then it seems like a class action would be a slam dunk and wouldn't cost you anything personally because class action lawyers are happy to skim millions off the top of the settlement.
I honestly don't know as I have never bought ads on FB. It would not surprise me if all but the biggest enterprise customers have horrible terms of service...
In practice FB's lawyers will produce a compelling bullshit excuse to explain the poor results, the fake clicks, the fake accounts, and the lack of sales.
Likely it will be the user's fault and FB can't be held responsible if the user keeps spending money etc etc.
This is really an antitrust issue, because it's a particularly nasty form of market monopolisation combined with cultivated mental and emotional manipulation to keep buyers locked in and spending.