It is part of a long-term Google strategy to pivot away from Android proper while still retaining the Android apps - and even some of those will be transitioned to PWAs - but again another story for another day. Google TV retains the OS - which again works fine - but is an entirely new platform/brand/strategy.
There is a story behind it but rather than bore you with it - it is irrelevant anyway - just suffice to say that Android TV (while working fine as an OS) is a failure as a platform, brand and strategy.
Android TV is going away in favor of Google TV. Why isn't it called Android TV? That is the 'technically' part. The primary mode of operation is having Netflix, Apple TV+ and other apps directly installed and executing on the device just as a Roku, Apple TV and Fire TV primarily work (with screen mirroring over AirPlay and DLNA being secondary). While Android TV devices like this do have Chromecast capability it is a secondary feature. This is (technically) an Android TV device. Although it features a similar set of functions to past Chromecast hardware, the new device features a new dongle-like design and comes packaged with a remote.
