I like how you trivialize it. Didn't they lose a ton of money, potentially their savings, because "their broker didn't accept their orders"?
Repeat that several times in your head, how does it sound?
This case will be a waste of time though.
The broker has to offer best efforts, but if something goes wrong and they can't execute the order then that's tough.
Even if that weren't true, this case hinges on whether those orders would have driven the price up (it didn't move much either way AFAIK). So to make the case, the class have to collectively admit to market manipulation. RobinHood stopping them was like a taxi driver refusing to drive robbers to the bank, the robbers don't get to sue when their dastardly plot is foiled! Or they can sue, but they'll lose and open themselves up further to prosecution!