The Apple tv fits into the Apple ecosystem. Watching a movie and your doorbell sees someone at the front door, you can have the Apple tv throw up a picture in a picture when it does. Get a FaceTime call? You can take it in your tv. Have a Facebook video on your phone? Flick it up to the tv.
Beyond that, the Apple tv has the superior processor so everything is always butter smooth and flawless. There are no ads, and Apple isn’t selling your data to anyone.
ring is amazon so it's alexa. But going to amazon and searching for homekit doorbell (or camera) will bring up several homekit compatible devices.
Alternatively, for things like uniquiti cameras, you can setup a homebridge server that will bring non homekit video feeds into homekit.