They're at least semi-scams. They get clicks by promising unrealistic returns to class members, such as 4 figures for the Caesars breach. Give me a fucking break.
I also don't see why they need to collect any info via these Facebook ads, as lawyers can subpoena the necessary info regarding who is in the class, without needing signups, in most cases. That's why you find yourself getting postcards for class action suits you didn't know existed, where indeed you were a member of the class from some previous business you did with the company.
Going back to the Caesars example, they don't need you to indicate that you were a member of Caesars Rewards. They should be able to get this info -- along with whose info was breached -- as part of the legal process.
I'm not sure what the exact angle here is, but I don't trust any of it. And there's now a ton of it on Facebook, all with dubious "class action" suits promising big returns, which I doubt will see the light of day.