Because it specifically says that "Congress shall make no law..."Where exactly does it state within the 1st amendment that this applies unless you're a private business???? Private business must also abide by the constitution...it is the supreme law of this country...
It does not say the people can say whatever they want wherever they want.
The first amendment was written to prevent the government from restricting the right of the people to speak freely about the government.
Basically it prevents the government from suppressing opposing views.
A private business can refuse service to anybody they want as long as it isn't based on race, religion, etc. A government agency can not do that. The Constitution sets the parameters for what the government can and can not do. Private businesses and citizens are governed by laws. The laws can't violate the Constitution or they will be voided.