Because the business is choosing who they use their resources to rebroadcast under their name and the government has a monopoly on violence. The government is

Because the business is choosing who they use their resources to rebroadcast under their name and the government has a monopoly on violence. The government is not guaranteeing that they will rebroadcast whatever you want to say, they are just not giving you consequences for saying it. Businesses aren't imposing consequences of violence on speech, they just are choosing not to be a part of it. Someone not listening to you is not censorship.