It's really not. It's so reviewers will be able to say "it costs more than the last version, but you also get much more storage" and the average consumer is happy. If there were a practical reason for it Apple would put it front and center.

They also bought RAC9, developers of Sneaky Sasquatch (one of the best games on the service, in my opinion), and they've had an aTV version since day one.

In general, the idea of a single game being able to hop between a phone (which can turn into a handheld with a controller grip), TV box, and desktop/laptop is really interesting. Streaming can do that, but latency and bandwidth caps become issues; this sidesteps it by letting you run everything locally.

That said, I'd love it if Plex or Jellyfin were able to use that storage to cache files locally (eg. stream the data as fast as possible and play from the local copy) to smooth out some flakiness with the wifi between the tv and my home server.

I'd guess it's room for the AI model and future versions of it that could grow.

I would expect only mobile developers to actually bother porting games natively to Apple TV, with larger titles opting for game streaming.