We used to get this all the time about the Ceiling Fan controls, until Google finally implemented CF controls from the app. We asked them repeatedly about it, but it’s unclear what effect our badgering had on their priorities.
Here’s how it works: we provide a manifest to Google Home with all the capabilities of the various devices that we make available to them. Then it’s up to Google how to make it work via voice and their app.
It’s not so much a choice of Google that it will not work in their app, they simply haven’t spent the resources to make the shades controllable from inside the app. I think they assumed that people would use voice with the voice assistants, not realizing that their app actually has a lot of potential for bringing all the devices in the home into one place.