I think there are two issues that you’re describing.
One is that Amazon, Google, Facebook and Twitter are essentially monopolies. Edit: that is to say that a lack of regulation seems to have pushed most of their competitors way down. If Twitter isn’t a monopoly then why the following lawsuit?
The Knight First Amendment Institute filed a new lawsuit against Trump for keeping several Twitter users blocked on his @RealDonaldTrump account.
www.politico.com
The other is that while it’s not technically a free speech issue, ”they” (the platforms above) are so ubiquitous a person running a business or a campaign without them is at a huge disadvantage.
My other thought on this independent of what I said above: our free speech is being used against us. Misinformation and deep fakes can easily be weaponized. It’s almost like the Internet needs fiction and nonfiction sections. Where does one draw the line between parody, satire, entertainment and purposeful deceit? Most people aren’t going to react to an Onion article, but most people believe if memed, it’s true.