I recall someone I knew that worked higher up in the US government scoffed at the idea of many of the "Government" conspiracies as not plausible due to the sheer incompetence of most government.
Getting them to tie their shoes in unison was difficult enough versus keeping some big secret from the public over the generations.
With the amount of stupid people in the general public as it is I just view it as incompetence as at fault most of the time versus big cover ups.
People also vastly overestimate how many people need to be in the known to participate in a conspiracy.
The chemical companies who dumped pfas into the environment fully aware of their problems had thousands of employees, how many of them do you think were part of the plan to keep it under wraps?
It's very easy to come up with excuses and string people along, you don't need to sit them around a table and explain your evil plot.