Can you call something a private company when they are the defacto monopolistic standard? What other video social media sites are there that eve remotely come close to competing?

When that happens, you're either basically a utility for the public, or a monopoly and need to be broken up. This whole concept that these "first amendment protects companies even though they control the market" reasonings are just absurd. It's exactly like defending the railroads for not wanting to ship black people because they don't have rails for "colored folk" and since they're a "private company" they can do what they want.