What’s stopping a sustained, constructive public inquiry into these parallels between past cover-ups and current information control?
There is no mechanism to promote the investigation. At best there will be queries like you made for the general, and social media reactions to specific events as they unfold.
A large chunk of government, politics, and press in the USA no longer exists. There are no authorities to turn too, now or later, regardless who gains power in Washington.
Most of the Anglosphere outside the USA is in a free fall too, a few years behind, maybe 20 years.