Not the person you originally applied to, but in my opinion this is most likely because corporations used to be extremely restricted in other aspects. Corporations were limited to operations listed in the charter they applied for and often could be immediately dismantled if they were found to be doing anything in violation of the law.

This mostly changed due to 'corporate personhood', the idea that corporations should have the same rights as people.

This article goes in to a lot of how this has lead to corporate abuses of power:

https://repository.uchastings.edu/hastings_law_journal/vol41...

This one's an easier read, but basically an editorial on the one above:

https://reclaimdemocracy.org/corporate-accountability-histor...

So that one private entity can tell another that they are talking out of their hat, and show them the door.

You have a right to free speech. You don’t have a right to force everyone to listen. What a fucking awful world that would be.

My initial reaction is to agree with you re: "fucking awful world", but I wanted to explore that a bit more. Would it actually be terrible if we had to allow people space to say what they want on a digital platform?

What would the side effects be of not being able to remove people from your store because they're behaving in a way you don't like? What if YouTube could not, legally, remove content that was "abusive" or "hateful"?

(Again, not saying I think this is how things should be, just trying to entertain the idea a bit.)

This needn't be posed as a hypothetical. There are places, both in the Internet zoo and in the real world, where you can go and look to see what this becomes.

Because the only communication platform (mail) was the government.

This is a little naive, you don't think private delivery services existed?

https://en.wikipedia.org/wiki/American_Letter_Mail_Company

That says founded 1844, over half a century from when the Bill of Rights was written.