Running in its own process, and, better yet, in its own cgroup (container) makes potential bugs in it, including RCEs, harder to exploit. It also makes it easier to limit resources it consumes, monitor its functioning, etc. Upgrading it does not require you to rebuild and redeploy your app, which may be important if a bug or performance regression occurs is triggered, and you need a quick upgrade or downgrade with (near) zero downtime.

Ideally every significant part should live in its own universe, only interacting with other parts via well-defined interfaces. Sadly, it's either more expensive (even as Unix processes, to say nothing of Windows), slower (Erlang / Elixir), or both (microservices).