The problem was not that they changed recommendations based on the knowledge available at the time, it's that those recommendations were not given with a qualification and confidence level appropriate to the strength of the data.

There was too much desire to appear strong and knowledgeable, resulting in too many occasions where forceful, even morally-based recommendations needed to be not just modified, but _reversed_ based on updated data (see the Surgeon General's tweet from Feb 29 on the uselessness and social immorality of mask use -- hasn't aged well).

To be fair, this was not all the CDC -- the media amplification / simplification played a huge role here also -- but the fact remains that the CDC and other US health authorities promulgated recommendations that were flat out wrong and in some cases actively harmful by overindexing on poor data.