Doctors depend on the free exchange of information to help their patients. It is one of the pathways that medicine advances. Covid was managed in a top down, hierarchical mode. Doctors who questioned it were threatened and punished by medical boards, some lost their licenses.
Had a non-vaccine treatment for covid been discovered via clinical practice it would have destroyed the EUA for the covid vaccine, i.e. that's how they were able to issue an experimental vaccine widely to the public. An effective covid treatment would have cost the corporations billions of dollars in the present, and the ongoing subscription income of annual covid vaccinations for hundreds of millions of people.
When you've got billions of income it's easy to spread it around to politicians, media, and scientists who are willing to carry the story. You just pay them well and make them sign NDAs: no one will talk. This forms a ready alliance to silence anyone who dares question the corporate narrative.