Developing Chromium OS for Raspberry Pi took about a little over 6 months to reach a usable state, alll that effort could only be used in the Pi build - in the ARM realm, there is no such “one image fits all” generic solution.
If there exists an Android TV box that has a community of over 5M people and could ship 640,000 units in a single month (March 2020), we will defintely consider it.