They operate under the extremely valuable liability protection granted them in section 230 of the CDA.
If I were to take government funds to build my warehouse, there's a pretty decent case that it is at least a public forum, if not a park.
>“In sum, the financial participation of the City in the Mall’s progress, the arrangements with the City police substation, and the active presence of other governmental agencies in the common areas of the Mall, constitute governmental involvement in the operation of the Mall,” the court noted. Thus, it concluded the mall’s “open and public areas ... effectively function as a public place,” and that mall owners couldn’t restrict distribution of political pamphlets or signature gathering in the mall’s common areas without violating the state Constitution.
Also, General Dynamics absolutely operates under many contractual obligations in which the federal government directly dictates how they shall run their business.
The Marsh line of decisions you're referring to was disposed of upthread. It's dead, Jim. SCOTUS just last year said you can't expect to pretend social networks operate as public squares; you can only claim functions that are normally exclusively the province of governments.
The basis for title 9 regulation is that universities take Federal grants.
https://en.wikipedia.org/wiki/Marsh_v._Alabama#Subsequent_hi...
Manhattan Community Access Corp. finds that _public access television stations_ aren't subject to the First Amendment, let alone private web hosts.
I mean, as an attorney, I think it would be kind of interesting to see what happened if the Supreme Court ruled that private web hosts in general, or Amazon in particular, are somehow state actors. It would be one of the most practically disruptive-to-society court decisions I can think of, about as interesting to watch as declaring that all warehouses are now public parks. But it's against both recent precedent and common sense.