I think it's just a pretty consolidated space? Kind of like ebook management, which was dominated by Calibre for so many years (this changed recently).

But unlike ebooks, media centre management is a fair bit more complex since it involves supporting many different media formats and many forms of acceleration or transcoding.

So the big projects - Kodi for local media and Jellyfin for streaming - have a lot of inertia because they tend to support whatever you throw at them.