It's a Python app, of course being distributed as a docker image is the sanest way of doing it. I don't see why you couldn't just pip install it if you really wanted, but having been a Python developer for close to two decades, I wouldn't want to.
That was the standard way a long time ago, and the first startup would take a really long time because it would install even more stuff. And sometimes fail. It wasn't very reliable if you used any addons, and some required a ton of extra steps that it couldn't automate like the modern deployments do now.
I happily ran a dockerized HA on a Debian for years now, no need to do any complicated debugging (and even if I did, it would not be difficult to inspect it properly)
