Because not all smart TV's support all apps including BT TV and BT Sport, etc nor do they all support YouTube HDR, all of these and others may work via the CCU.
This is why I haven't quite been able to justify buying one. Not at full price anyway and not even at this price I think. Maybe if they become cheaper. I have a 4K TV with all the apps. The only disappointing thing so far is the quality of Google Play Movies (same problems whether I use the Play Movies app or the YouTube app). The Ultra may improve on that but I rarely watch a Google Play Movie. The other thing that would be nice would be to cast Google Photos. But, again, not quite worth the cost. I do like the idea of Google Assistant integration but that seems limited in this case. So, even though I'm the OP, I fear I must be sensible and hold off!
Just tried it, managed to put my TV to sleep even without the Chromecast channel being on. I normally shout to it and ask it to play things from Netflix. Works most of the time, especially for the regular shows I watch.
Genuine question: I'm assuming people looking to buy this have a 4K TV. Most if not all 4K TVs I think have 4K apps for services like Netflix. Therefore why would anyone need to buy this? Btw: I have a standard Chromecast I use on my old TV that doesn't have inbuilt apps.
Not worth it then. Need HLG.