But these aren’t just private entities. They use public airwaves. They used public research, etc. The courts in the past have ruled that a mall (ie private property) could not exclude people who wanted to hold political protests on their property because they were effectively the town square.
It was the same in company towns - they too could not exclude people from protesting, signing petitions, etc on their property even though they were private companies because they owned the whole town and thus could not exclude people from the town square.
In the modern era, social media is the digital town square.