This is a popular meme, but I'm not certain it's true. Given how many people use Twitter, Reddit, Tiktok, Twitch, Instagram, Discord, etc, it doesn't seem as if they're somehow also unaware that the rest of the web or alternative means of communication exist.
I mean, Donald Trump literally just started his own "social media platform," and his followers have been bouncing around right-wing "alternative" platforms for years. Not even the people primarily responsible for pushing the fear narrative around social media and it's "Orwellian" control of free speech really seem to be suffering under its hypothetical jackboot.
There's exactly one, maybe two of each for each type of media. Twitter for soundbits, Tiktok for video, Instagram for photo - in the past you had your choice of publishers. If one didn't like you you could go to another and at least get the message out. I'm seeing the concentration in the media market with great concern, it gives excessive power to shape opinion to a few magnates. The Trump ban is just a symptom.
We seem to be living in different realities. Where you're seeing media concentrating, I'm seeing it fragmenting and diverge. The big social media silos are popular, but that popularity doesn't translate to control of the medium.