Ever since the Chromecast with Google TV came out I've been waiting for a more global rollout. Sadly, it looks like no new markets have been added since. Also in the settings I still can only add Netflix and my Prime account while other major services (like HBO and Disney) are freely available here. Are there any rumours of this become a more global feature anytime soon?
Google is still not selling the device everywhere, and they are trying to get media-companies to integrate further before pushing it further in some areas. As you notice the user-experience is so-so when you dont have those integrations.
There are different levels of integration you can choose to do as a streaming-service, that will affect how your content will be visible/searchable in GoogleTV/Google search/Home. Its optionable, but if you dont you wont get any "retail-space" in the most important positions.
Basically its about loss of control vs. better content discovery. Netflix pulled parts of their integration very fast after launch of GoogleTV, probably because they believe Google is positioning themselves as the new distributor that have 100% control and as a result that would mean users wouldn't open the Netflix app to browse content anymore. Instead users will primarily use the GoogleTV interface, and then Netflix will not have the same technical/experience advantage they have had until now over almost all other services out there. The playing field will be more level, but instead Google will have most of the control.
If you want to read up on the choices media-companies have you can do it here . But basically its about sharing metadata about the content in a certain way to Google, so your content can be indexed and made searchable. But depending on what info you give them that affects the user experience in relation to features like "View-next episode", "Do I already have a subscription giving access", shared login, voice casting, search etc.