To restrict or to otherwise remove the certificate of airworthiness implies that you have probable knowledge of the the degree of restriction necessary or violation of the original certificate.
That has not yet been concluded by the investigation or the regulator
It was presumed that any fleet entering service does so by carrying a degree of latent unknown risk. Historical hindsight has shown that this degree can vary over time with some risks maturing into known risks which are then addressed over time by minimizations and corrective action programs, while still newer risks develop.
The issue is not which ones are latent unknowns and which ones are known and being addressed over time, but rather the question is how much risk is being carried over what period of time.
Restrictions and/or groundings are decided on the level of risk and not just whether the total risk causes are known or unknown.