Clearchannel, which controlled most FM channels, infamously stopped playing John Lennon's "Imagine" after Sep 11 2001. So this is not new. In the absence of popular govt. media and channels, this does form de facto censorship in the US.

The usual explanation I have heard is that free speech is limited to tge govt. not able to arrest you for criticising it. It does not apply to private parties.

I think de facto censorship by private monopolies must also be illegal for true freedom of speech.