I share your sentiment on YouTube TV. However, I do not think it's reasonable to expect any random Android app to work on Android TV.... Completely different UI.

Hey I just bought an Apple TV - why don't my iOS Apps work in the Apple TV's tvOS - I mean C'mon both have "OS" in their names !!!

;-) ;-) ;-)

Apple TV has all of the same apps from phone to Apple TV

No it doesn't. They're developed separately just like on Android and Android TV.

Why wouldn't you have done your homework prior to buying one? Android TV ≠ Android and Google haven't been shy about that fact.

You can try to "sideload" the apps that you can't find on the android tv play store.

Sideloadind means that you download the application installation .apk file from the web and then install it just like you do on your phone.

This can end up with total victory like when I downloaded the official mobile port of sonic 1 and 2, and noticed that they worked perfectly with controllers.

Or you can end up with app that is barely usable with usb mouse or some kind of air mouse remote. Or some apps will not boot at all.

You can also go to the play store on your computer browser and then choose to download the app in your shield tv console. Some apps and games that aren't in the actual android tv play store can still be downloaded from the website and those usually at least work with the air mouse if not with the normal remote as well.

Interesting. I have a Google Nexus Player and it has a YouTube app through the Google Play store. Don't know if it runs the same OS as the shield.