You can decouple Postgres and surrounding userspace upgrade cycles from your host os, if this is something that you want. Or run multiple different PG versions (have independent upgrades schedule) without being tied to the host os specific mechanisms for that.

It makes the whole thing is configured in a docker-compose file (or your raw Docker CLI invocation) + the data volume. So as long as you have those two things you can replicate it and move it to other hosts regardless of their distro.

Compare that with using your distro's packaged version where you can have version variations, variations in default config or file path locations, etc.