Scientists must be careful in how they communicate, and organizations like the CDC and FDA need to staff expert scientific communicators who can explain complicated things to lay people. Bill Nye types.
"Vaccines contain dihydrogen monoxide, a chemical that killed over 200,000 people within hours in 2004" is a scientifically factual statement, but not a well communicated one.
Imagine a scientist with significant political cachet. This allows them to receive more funding, do more science. They cannot optimize their behavior only for truth-seeking, because that fails to maximize their political capital. If they optimize for the former, they will be replaced by someone who is better at the latter.
Any scientist that relies on external funding must balance science with politics to continue to do science, sometimes this involves censorship.