They do this so a manufacturer can use the same parts among different products or simply install an upgraded one to unlock more features.
If it were standardized, this would be fairly easy given that they all pretty much work the same but then they would have write actually good software and UI for people to elect to use their specific product.
You could have 2 tiers of board: Essentials, which is cheap and only has as much hardware and software as is strictly necessary to produce a pre-smart-TV experience, and Deluxe which would be pricier and built around a recent flagship SoC (e.g. Snapdragon 8 Gen 1/2/3) with an unlocked bootloader and preloaded with Android TV.
> 24V for the display
Cathode Ray Dude has a few episodes about them.
https://youtu.be/q9a3dCd1SQI?t=2006
They're called Open Pluggable Specification Modules.
Like, I don't want to plug a chromecast into my "old" tv to "upgrade" it and having to live with a second remote control and more batteries, plugging another device to the electricity outlet and being able to use it only with wifi while the ethernet port of the TV is now rendered useless - I'd really like to be able to upgrade its internals without having to go broke while buying a new one.