These are niche use cases. Most TV manufacturers install Roku, FireTV or GoogleTV.
Those that had their own OS have mothballed it, Roku is being replaced with GoogleTV as the default Smart TV OS of choice by many manufacturers and FireTV is just a custom skin of GoogleTV. Amazon is the primary driver for FireTV as TizenOS is for Samsung. In this space the present clear winner is GoogleTV for tv manufacturers and with that comes developer investment.
I am sorry if Apple is unable to innovate in this space why even bother, if a consumer is on a budget and many are, do you think those consumer will opt for a plus $100 set top box from Apple or just use what’s built-in the TV which is GoogleTV with AirPlay included. Many consumer just play mobile games and the built-in hardware spec do a fine job. If anyone is into serious gaming it’s either a dedicated gaming console or a PC, Apple is high on its own smoke and drunk on its own Kool-Aid.
At this point it might as well cut deals with TV manufacturers to have it run TvOS as a form of advertising but Google beat them to the punch.
You're making a different argument than the one I was engaged in with what I wrote. I was replying to someone saying that the Apple TV is way behind other STBs like the Shield. It's not, it's different. What you wrote is an argument for why so many people aren't buying STBs to begin with.
The answer is the same though...
Just like Apple isn't going to launch a product like the Shield which prioritizes things other than streaming/subscription content, Apple isn't going to develop tvOS for 3rd party TVs. They don't do this with PCs, with phones, watches, tablets or anything else they do.
The Apple TV remains, by far, the best box in terms of UI and UE for the Apple ecosystem and online streaming/subscription services and also is better in that regard than anything built in to smart TVs. That's the niche they've carved out of the market and they're not going to deviate from that anytime soon.
Want games: Playstation, Xbox.
Want high-end audio from remuxed Blu-Ray: Shield.
Want best video options, best UI, and best UE if in Apple ecosystem: Apple TV.
Want to be cheap about all of this: use what's built into your TV.