In the US, it's because a bunch of demagogues have decided that they will make a lot of money (or retain political power) by saying that vaccines don't work and/or are harmful. Fox News regularly spews this kind of nonsense in its programming and a number of Republican politicians are happy to go along with it.
> We should remember that the freedom of the press exists because a well informed population is necessary for a functioning democracy.
The text of the First Amendment does not contain this or any other justification for itself. And rightfully so I think; such a right does not require utilitarian justification.
"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."
