What I mean: Since they all signed NDAs they are not allowed to openly criticize their company—ever. Not when being hired and not after being fired. Since 173 were fired it's easy to ignore NDAs because they won't get caught. But it's not right, they break a significant agreement and this is so typical for employees (just head to Glassdoor and how much internal stuff is disclosed).
Every employment contract has by nature a NDA embedded. And those are much stricter than dedicated NDAs since employment contracts get rarely negotiated line by line, most employees just accept and sign employment contracts.
tl;dr obvious fact > nda > deals behind closed doors
Companies where employees actually keep secrets do so by earning the trust and respect of their employees, not by writing ironclad employee agreements.
In this particular case, for these employees, I think it boils down to whether they honor their loyalty to the company vision more than their employee agreement.