[zuminator]

Pluto TV is owned by ViacomCBS and Tubi is owned by the Fox Corporation (the non-Disney one), and as others have pointed out, all their content is licensed. There's also Xumo, owned by Comcast. Pluto TV has partnership deals with Roku, Vizio and others to provide them with content for their branded apps. Amazon has a somewhat similar service with IMDb TV, although it has a crappy interface modeled off Amazon Prime's. And of course even Plex has now (sadly) entered the game with their "Live TV" section.

What annoys me about these free offerings is that they have cannibalized their content from paid streaming services. Before, services like Hulu and Amazon Prime would stock their catalog with tons of old "classic" TV shows that you could binge commercial free. Now, the only way to stream many of those shows is with commercials, they are no longer available as part of any paid commercial-free packages, unless you are willing to purchase the individual episodes.