It's not about being informed; it's about general knowledge.

If it were about being informed, the plaintiff could attest "I was not informed" which would be reasonable in a court as they're talking about what they have direct experience of. But they defence is saying "you may not have been specifically informed, but you should have known anyway because it was in the news."

The plaintiffs did not say "there was no general awareness of these problems" - had they done so, maybe that would have been sufficient, or more likely they would have needed to enter evidence like statements from a sufficiently broad body of customers. But they didn't do that, so they didn't contest the argument which the judge decided was at least enough if was true.

The real question here is whether "general awareness of issues" is enough to defend cases like these.