What's stopping someone else from copying the lawsuit?
(Sorry couldn’t resist)
If you didn’t, then you can bring your own suit. But in order to bring a suit you’d have to show you’ve been harmed, so you’d have to have been a customer of one of these printers.
For instance you buy a dishwasher that is faulty. There’s a class action settlement, but for you, the dishwasher ruined your apartment and the neighbors downstairs. You can opt out and sue directly even if there’s been a class settlement.